PROF. J. F. ELSOM.

" The science of Geology illustrates many astonishing facts." Viewed in the light of authentic tests, the region of country over which this work extends, presents ample study for the Geologist and Antiquarian, for nowhere in the broad expanse of country traversed by the writer--excepting, perhaps, some sections of the country of mines--is there such a fine field for the labor of the geologist. As we stood upon the high bluffs viewing the beautiful valleys below, or rowed over any of these streams--commercial arteries of this great country--and tried to peer up the steep sides of the overhanging bluffs, we often imagined ourself living away amid the dim cycles of the past; again we lived in the present, wondering what unseen agencies and gigantic forces had been employed to transform what was evidently once a vast and almost boundless sea, into one of the finest sections of land--food producing land--between the two great oceans. Again, as the author examined with hammer and chisel, testing the chips by heat and cold, acid and alkali, subjecting the fused residuum to the diaphragm of the microscope, or the wonderful spectra of the spectroscope, he was often amazed at the broad expanse of time that must have elapsed to make this wonderful strata from that ungainly, shapeless mass, which, as Sacred History teaches, was this earth's original form. Furthermore, it seems almost incredible that little by little as these sands accummulate, that there could have elapsed sufficient time for these marine aggregations and changes. This, however, is merely prefaratory, and we must hasten on to the subject matter, accorded to this limited space, for to do the subject anything like justice, a book much larger than this entire history would be required. The reader will know by this why we have not gone more into detail in our discussion of this interesting and valuable portion of the work.

To the geologist, among the first things to attract the attention in this section is the "Walled Lakes" of Northern Iowa, one of them in Wright County--where we first mad a survey--is about three-eighths of a mile wide, with a wall or embankment form 2 to 10 feet high surrounding it, formerly supposed to be the work of ancient races, a theory, however, now discountenanced, for practical tests and observation go to prove that they are the results of natural causes, namely the periodical action of alternate heat and cold, aided to a limited extent by the action of the waves. These little lakes are very shallow, and during the ordinary winter freeze nearly solid, so that little or no water remains at the bottom, but

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a little will generally be found in the middle. As a consequence all loose substances at the bottom adhere to the ice below, and the expansive power of water when freezing--which must be immense in such a body as some of these lakes--acts equally in all directions from the center of the circumference, and annually whatever was on the bottom of the lake has by this means been carried to the shore. This process, imperceptible, perhaps, to the casual observer in a single season, has been going on from year to year, century after century, causing these embankments, formerly a great wonder to everyone, but perfectly simple to any and all, if the various strata of the walls be carefully examined and compared with each other

The entire State contains very few what may be classed as large elevations, the highest point being but a trifle over twelve hundred feet higher than its lowest point as shown by barometrical surveys; there are two such points, and are nearly three hundred miles apart; then if we think for a moment, it will be seen the entire State is traversed by gently flowing rivers--rapids nearly unknown--hence we have the entire State resting entirely within, comprising a part of a vast plain, with no mountain or hill range within its limits.

A further idea of the general uniformity which characterizes the State may be gleaned from the survey from point to point, and the following statement of the general slopes in feet per mile, in straight lines across:

From the NE corner to the SE corner 1 foot 1 inch per mile.
From the NE corner to Spirit Lake 5 feet 5 inches per mile.
From the NW corner to Spirit Lake 5 feet per mile.
From the NW corer to the SW corner 2 feet per mile.
From the SW corner to the highest ridge 4 feet 1 inch per mile.
From the dividing ridge to the SE corner 5 feet 7 inches per mile.
From the highest point in the State to the lowest 4 feet per mile.

This statement shows a great uniformity, and a good degree of propriety in estimating the whole State as part of a great plain, the lowest point showing but 144 feet above sea level. This point, nearly at the mouth of Des Moines River, presents a geological formation of great interest, but being so far removed from the territory within the scope of the work we will not discuss it in this connection. Taking the highest point--near Spirit Lake--and the lowest point--near the mouth of the Des Moines--gives but a slight elevation and depression, and a general average of the entire State of eight hundred feet above the level of the sea, though from the nearest point the State is over a thousand miles from the sea coast, a rather remarkable instance, and another proof of being a part of a vast plain. Of course, when we consider the slightly diversified surface of Western Iowa, the formation of small valleys out of the general level, which have been evolved by the action of streams, lakes, etc., during the dim cycles of the past, it

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may appear a trifle jejune, but will not alter the general and accepted theory aforesaid. Especially is this true with reference to the northwestern portion, the seeming deviation being much more apparent in the northeastern portion of the State.

It will be well enough to mention that the Missouri River, though washing as many or more miles of Iowa's shore than the Mississippi, drains but about one-third of its surface, going to partially prove that this plain of which we speak, extends away out in Nebraska, where we have unmistakable evidences of the Missouri having once threaded its course, the other side being about one and two-thirds broader than the State.

Thus much with reference to the surface indications. We will now go lower and see what can be found beneath this beautiful and somewhat phenomenal exterior.

In our tests of the soil, we will make but three general divisions, which of themselves not only differ in their physical character, but are widely separated in their ultimate origin. These will be classed as drift, bluff, and alluvial, and belong respectively to the deposits bearing the same names, the first of which occupies over two-thirds the surface of the entire State.

Every person who has paid the least atention [attention] to any of the analytical sciences, so-called, knows that when we speak of soil, in the general acceptation of the term, that we mean disintegrated or powdered rock.

The drift deposit of Iowa was derived, to a considerable extent, from the rocks of Minnesota; but the greater part of Iowa drift was derived from its own rocks, much of which has been transported but a short distance. In general terms the constant component element of the drift soil is that portion which was transported from the north, while the inconstant elements are those portions which were derived from the adjacent or underlying strata. For example, in Western Iowa, wherever that cretaceous formation known as the Nishnabotany sandstone exists, the soil contains more sand than elsewhere. The same may be said of the soil of some parts of the State occupied by the lower coal measures, the sandstones and sand shales of that formation furnishing the sand.

We find upon examination, however, that in the section of Iowa of which this work treats, the drift contains more sand and gravel than any other portion of the State. There is no question in my mind but this was derived from the cretaceous rocks that now do, or formerly did exist, and also in part from the conglomerate and pudding stone beds of the Sioux quartzite.

The bluff soil, then, is that which rests upon, and constitutes part of the bluff deposit, and is found only in the western portion along the Missouri River. Chemical analysis shows but one per cent., generally less, of alumina, at the same time it contains other constituent elements which render it little, if any inferior for

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agricultural purposes; a very large portion of it is far out of reach of the highest floods, and must be very productive.

We now come to the alluvaial. This is that portion called the flood plains of the river bottoms or valleys. That portion periodically flooded by the rivers, of course, is thereby rendered comparatively valueless for agricultural purposes for apparent reasons; but much of it, we might say by far the larger portion, is beyond the reach of floods, and is very rich in those elements which enter into plant life.

Speaking more properly of the geology of this particular section of Iowa, we find the rocks to range all along from the Azoic to the Merazoic inclusive. Taking the State as a whole, the surface is generally occupied by the evidences of the Palæzoic age. The following tabular statement gives each of these formations in the order in which they occur:

SYSTEMS. AGES	GROUPS PERIODS	FORMATIONS EPOCHS	THICKNESS IN FEET
Cretaceous Carboniferous.. Devonian...... Upper Silurain.. Lower Silurian. Azoie	{Post Tertiary.... {Lower Cretaceous{ {Coal Measures{ {Subcarboniferous{ Hamilton........ Niagara......... {Cincinnati....... {.....Trenton...... {.....Primordial... Huronian.......	Drift Inoceramous bed Woodbury Sandstone; Shales Ishnabotany Sandstone Upper Coal Measures Middle Coal Measures Lower Coal Measures St. Louis Limestone Keokuk Limestone Burlington Limestone Kinderhook beds Hamilton Limestone and Shales Niagara Limestone Maquoketa Shales Galena Limestone Trenton Limestone St. Peter's Sandstone Lower Magnesian Limestone Potsdam Sandstone Sioux Quartzite	10to200 50 130 100 200 200 200 75 90 196 175 200 350 80 250 200 80 250 300 50

We now arrive at what is known and recognized by the specific name of Sioux quartzite, and is found exposed in natural ledges, only in a few spots away up in the extreme northwestern part of the State, upon the banks of the Big Sioux River, which position doubtless gave it its local name. This rock is intensely hard, disintegrates in sort sort of splinters; its color varying according to locality from nearly a yellow to a deep red. One thing connected with this rock is its process of metamorphism, which has been so complete all through the entire formation wherever found. Whether exposed to

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the surface or hidden hundreds of feet below the surface, the rock is found to be of almost uniform texture. As far as we have been able to examine, the dip is found to be from 4.75 to 5.20 degrees and northward, but the trend of the outcrop is to the eastward and westward. In some rare cases the rock is profitably quarried, but generally speaking, it is very difficult to secure it in dry forms, except that into which it naturally cracks, and the tendency is into angular places. I have found the samples sent to be absolutely indestructible.

There are many other systems, of themselves very interesting to the scientific reader and investigator, but our limited space stands as an insurmountable barrier; hence we will have to pass the Lower Silurian system in the Primordial group of the eastern part of the State; it, however, is valueless for building purposes, and contains few if any, fossils. Then we have the Lower Magnesian Limestone, found but little here, containing a few crinoids and smaller fossils. Following this in point of interest, is the St. Peter's Sandstone, which exists in uniform thickness throughout the State where found, which is beneath the drift.

Of the Trenton Group of the Upper and Lower Sillurian age, but little interest to anyone can be said, save that it contains a great variety of fossils, and it makes very ornamental stone for cap and window sills. In this section of the State the drift contains more silex and gravel than elsewhere, as before stated, but in those sections where fossils are found, they are new to all I have read of science, open new fields of thought and investigation, and are found peculiar to the Hawkeye State.

Passing again the Galena Limestone of Dubuque, and other counties: This is always the upper formation of the Trenton Group. It seldom extends over twelve miles in width, though fully one hundred in length. In Dubuque County the greatest development of this limestone is exhibited. It is found to be merely a pure dolomite, with an occasional slight admixture of silicious matter. It is almost worthless for dressing; its principal value consisting of its formation being the source of lead ore, but the lead region of Iowa is confined to an area of say fifteen miles square. The one occurs in vertical fissures, which traverse the rock at regular intervals from east to west; some, however, is found in those which have a north and south course. Very small quantities of what is known as carbonate are found in it; its principal being what assayers call sulphuret of lead.

Probably one of the most important of all the geological formations of the State is the Coal-Measure group. This is divided into three formations, viz., the lower, middle and upper coal measures, each having a vertical thickness of about two hundred feet.

A line drawn upon the map of Iowa as follows, will represent the eastern and northern boundaries of the coal fields of the State: Commencing at the southeast corner of Van Buren County, carry

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the line to the northeast corner of Jefferson County by a slight easterly curve through the western portions of Lee and Henry Counties. Produce this line until it reaches a point six or eight miles northward from the one last named, and then carry it northwestward, keeping it at about the same distance to the northward of Skunk River and its north branch that it had at first, until it reaches the southern boundary of Marshall County, a little west of its center. Then carry it to a point three or four miles northeast of Eldora, Hardin County; thence westward to a point a little north of Webster City, in Hamilton County; and thence further westward to a point a little north of Fort Dodge, in Webster County.

In consequence of the recedence to the southward of the borders of the middle and upper coal measures, the lower coal measures alone exist to the eastward and northward of Des Moines River. They also occupy a large area westward and southward of that river, but their southerly dip passes them below the middle coal measures at no great distance from the river.

No other formation in the whole State possesses the economic value of the lower coal measures. The clay that underlies almost every bed of coal furnishes a large amount of material for potters' use. The sandstone of these measures is usually soft and unfit, but in some places, as near Red Rock, in Marion County, blocks of large dimensions are obtained which make good building material, samples of which can be seen in the State Arsenal at Des Moines. On the whole, that portion of the State occupied by the lower coal measures, is not well supplied with stone.

But few fossils have been found in any of the strata of the lower coal measures, but such animal remains as have been found are without exception of marine origin.

Of fossil plants found in these measures all probably belong to the class acrogens. Specimens of calamites, and several species of ferns are found in all the coal measures, but the genus lipedadendron seems not to have existed later than the epoch of the middle coal measures.

This formation within the State of Iowa occupies a narrow belt of territory in the southern central portion of the State, embracing a superficial area of about fourteen hundred square miles. The counties more or less underlaid by this formation are Guthrie, Dallas, Polk, Madison, Warren, Clarke, Lucas, Monroe, Wayne and Appanoose.

This formation is composed of alternating beds of clay, sandstone and limestone, the clays or shales constituting the bulk of the formation, the limestone occurring in their bands, the lithological peculiarities of which offer many contrasts to the limestones of the upper and lower coal measures. The formation is also characterized by regular wave-like undulations, with a parelleism which indicates a widespread disturbance, though no dislocation of the strata has been discovered.

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Generally speaking, a few species of fossils occur in these beds. Some of the shales and sandstone have afforded a few imperfectly preserved land plants--three or four species of ferns, belonging to the genera. Some of the carboniferous shales afford beautiful specimens of what appear to have been sea-weeds. Radiates are represented by corals. The mollusks are most numerously represented. Trilobites and ostracoids. are the only remains known of articulates. Vertebrates are only known by the remains of salachians, or sharks, and ganoids.

The area occupied by this formation in Iowa is very great, comprising thirteen whole counties, in the southwestern part of the State. It adjoins by its northern and eastern boundaries the area occupied by the middle coal measures.

The prominent lithological features of this formation are its limestones, yet it contains a considerable proportion of shales and sandstones. Although it is known by the name of upper coal measures, it contains but a single bed of coal, and that only about twenty inches in maximum thickness.

The limstone exposed in this formation furnishes good material for building as in Madison and Fremont counties. The sandstones are quite worthless. No beds of clay for potters' use are found in the whole formation.

The fossils in this formation are much more numerous than in either the middle or lower coal measures. The vertebrates are represented by the fishes of the orders selachians and ganoids. The articulates are represented by the trilobites and ostracoids. Mollusks are represented by the classes cephlopoda, gasteropoda, lamelli, branchiata, brachiapoda polyzoa. Radiates are more numerous than in the lower and middle coal measures. Protogoans are represented in the greatest abundance, some layers of limestone being almost entirely composed of their small fussiform shells.

There being no rocks, in Iowa, of permian, triassic or jurassic age, the next strata in the geological series are of the cretaceous age. They are found in the western half of the State, and do not dip as do all the other formations upon which they rest, to the southward and westward, but have a general dip of their own to the north of westward, which, however, is very slight. Although the actual exposures of cretaceous rocks are few in Iowa, there is reason to believe that nearly all the western half of the State was orginally occupied by them; but being very friable, they have been removed by denundation, which has taken place at two separate periods. The first period was during its elevation from the cretaceous sea, and during the long tertiary age that passed between the time of that elevation and the commencement of the glacial epoch. The second period was during the glacial epoch, when the ice produced their entire removal over considerable areas.

It is difficult to indicate the exact boundaries of these rocks; the following will approximate the outlines of the area:

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From the northeast corner to the southwest corner of Kossuth County; thence to the southeast corner of Guthrie County;; thence to the southeast corner of Cass County; thence to the middle of the south boundary of Montgomery County; thence to the middle of the north boundary of Pottawattamie County; thence to the middle of the south boundary of Woodbury County; thence to Sergeant's Bluffs; up the Missouri and Big Sioux Rivers, to the northwest corner of the State; eastward along the State line to the place of beginning.

All the cretaceous rocks in Iowa are a part of the same deposits farther up the Missouri River, and in reality from their eastern boundary.

Nishnabotany Sandstone.--This rock has the most easterly and southerly extent of the cretaceous deposits of Iowa, reaching the southeastern part of the Guthrie County and the southern part of Montgomery County. To the northward, it passes beneath the Woodbury sandstones and shales, the latter passing beneath inoceramus, or chalky, beds. This sandstone is with few exceptions, almost valueless for economic purposes.

The only fossils found in this formation are a few fragments of angiospermous leaves.

Woodbury Sandstones and Shales.--These strata rest upon the Nishnabotany sandstone, and have not been observed outside of Woodbury County, hence their name. Their principal exposure is at Sergeant's Bluffs, seven miles below Sioux City.

This rock has no value except for purposes of common masonry.

Fossil remains are rare. Detached scales of lepidoginoid species have been detected, but no other vertebrate remains. Of remains of vegetation, leaves of salix meekii and sassafras cretaceum have been occassionally found.

Inoceramus beds.--These beds rest upon the Wood bury sandstones and shales. They have not been observed in Iowa, except in the Bluffs which border the Big Sioux River in Woodbury and Plymouth Counties. They are composed almost entirely of calcareous material, the upper portion of which is extensively used for lime. No building material is to be obtained from these beds; and the ony value they possess, except lime, are the marls, which at some time may be useful on the soil of the adjacent region.

The only vertebrate remains found in the Cretaceous rocks are the fishes. Those in the inoceramus beds of Iowa are two species of squoloid selachians, or cestratront, and three genera of teliosts. Mossuscan remains are rare.

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Extensive beds of peat exist in Northern Middle Iowa, which, it is estimated, contain the following area:

Counties.	Acres.
Cerro Gordo	1,500
Worth	2,000
Winnebago	2,000
Hancock	1,500
Wright	500
Kossuth	700
Dickinson	80

Several other counties contain peat beds, but the character of the peat is inferior to that in the northern part of the State. The character of the peat named is equal to that of Ireland. The beds are of an average depth of four feet. It is estimated that each acre of these beds will furnish two hundred and fifty tons of dry fuel for each foot in depth. At present, owing to the sparseness of the population, this peat is not utilized; but, owing to its gret distance from coal fields and absence of timber, the time is coming when their value will be realized, and the fact demonstrated that Nature has abundantly compensated the deficiency of other fuel.

GYPSUM

The only deposits of the sulphates of the alkaline earths of any economic value in Iowa are those of gypsum at, and in the vicinity of Fort Dodge, in Webster County. All others are small and unimportant. The deposit occupies a nearly central position in Webster County, the Des Moines River running nearly centrally through it, along the valley sides of which the gypsum is seen in the form of ordinary rock cliff and ledges, and also occurring abundantly in similar positions along both sides of the numerous ravines coming into the river valley.

The most northerly known limit of the deposit is at a point near the mouth of Lizard Creek, a tributary of the Des Moines River, and almost adjoining the town of Fort Dodge. The most southerly point at which it has been found exposed is about six miles, by way of the river, from this northerly point before mentioned. Our knowledge of the width of the area occupied by it is limited by the exposures seen in the valleys of the small streams and in the ravines which come into the valley within the distance mentioned. As one goes up these ravines and minor valleys, the gypsum becomes lost beneath the overlying drift. There can be no doubt that the different parts of this deposit, now disconnected by the valleys and ravines having been cut through it, were originally connected as a continuous deposit, and there seems to be as little reason to doubt that the gypsum still extends to considerable distance on each side of the valley of the river beneath the drift which covers the region to a depth of from twenty to sixty feet.

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The country round about this region has the prairie surface approximating a general level which is so characteristic of the greater part of the State, and which exists irrespective of the character or geological age of the strata beneath, mainly because the drift is so deep and uniformly distributed that it frequently almost alone gives character to the surface. The valley sides of the Des Moines River, in the vicinity of Fort Dodge, are somewhat abrupt, having a depth there from the general level of the upland of about one hundred and seventy feet, and consequently presents somewhat bold and interesting features in the landscape.

As one walks up and down the creeks and ravines which come into the valley of the Des Moines River there, he sees the gypsum exposed on either side of them, jutting out from beneath the drift in the form of ledges and bold quarry fronts, having almost the exact appearance of ordinary limestone exposures, so horizontal and regular are its lines of stratification, and so similar in color is it to some varieties of that rock. The principal quarries now opened are on Two Mile Creek, a couple of miles below Fort Dodge.

The reader will please bear in mind that the gypsum of this remarkable deposit does not occur in "heaps" or "nests" as it does in most deposits of gypsum in the States farther eastward, but that it exists here in the form of a regularly stratified, continuous formation, as in uniform in texture, color and quality throughout the whole region, and from top to bottom of the deposit as the granite of the Quincy quarries is. Its color is a uniform gray, resulting lines of darker shade. The gypsum of the white lines is almost entirely pure, the darker lines containing the impurity. This is at intervals barely sufficient in amount to cause the separation of the mass upon those lines into beds or layers, thus facilitating the quarrying of it into desired shapes. These bedding surfaces have occasionally a clayey feeling to the touch, but there is nowhere any intercalaton of clay clay or other foreign substance in a separate form. The deposit is known to reach a thickness of thirty feet at the quarries referred to, but although it will probably be found to exceed this thickness at some other points, at the natural exposures, it is seldom seen to be more that from ten to twenty feet thick.

Since the drift is usually seen to rest directly upon the gypsum, with nothing intervening, except at a few points where traces appear of an overlying bed of clayey material without doubt of the same age as the gypsum, the latter probably lost something of its thickness by mechanical erosion during the glacial epoch; and it has, also suffered some diminution of thickness since then by solution in the waters which constantly percolate through the drift from the surface. The drift of this region being somewhat clayey, particularly in its lower part, it has doubtless served

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in some degree as a protection against the diminution of the gypsum by solution in consequence of its partial imperviousness to water. If the gypsum had been covered by a deposit of sand instead of the drift clays, it would have no doubt disappeared by being dissolved in the water that would have constantly reached it from the surface. Water merely resting upon it would not dissolve it away to any extent, but it rapidly disappears under the action of running water. Where little rills of water at the time of every rain run over the face of an unused quarry, from the surface above it, deep grooves are thereby cut into it, giving it somewhat the appearance of melting ice around a waterfall. The fact that gypsum is now suffering a constant, but, of course, very slight diminution, is apparent in the fact the springs of the region contain more or less of it in solution in their waters.

Besides the clayed beds that are sometimes seen to rest upon the gypsum, there are occasionally others seen beneath them that are also of the same age, and not of the age of the coal-measure strata upon which they rest.

In neither the gypsum nor the associated clays has any trace of any fossil remains been found, nor has any other indication of its geological age been observed, except that which is afforded by its stratigraphical relations; and the most that can be said with certainty is that it is nearer than the coal measures, and older than the drift. The indications afforded by the stratigraphical relations of the gypsum deposit of Fort Dodge are, however, of considerable value.

As already shown, it rests in that region directly and unconformably upon the lower coal measures; but going southward from there, the whole series of coal-measure strata from the top of the subcarboniferous group to the upper coal measures, inclusive, can be traced without break or unconformability. The strata of the latter also may be traced in the same manner up into the Permian rocks of Kansas; and through this long series, there is no place or horizon which suggests that the gypsum deposit might belong there.

Again, no Tertiary deposits are known to exist within or near the borders of Iowa to suggest that the gypsum might be of that age; nor are any of the palæozoic strata newer than the subcarboniferous unconformable upon each other as the other gypsum in unconformable upon the strata beneath it. It therefore seems, in a measure, conclusive, that the gypsum is of Mesozoic age, perhaps older than the Cretaceous.

LITHOLOGICAL ORIGIN

As little can be said with certainty concerning the lithological origin of this deposit as can be said concerning its geological age, for it seems to present itself in this relation, as in the former one

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as an isolated fact. None of the associated strata show any traces of a double decomposition of pre-existing materials, such as some have supposed all deposits of gypsum to have resulted from. No considerable quantity of oxide of iron nor and trace of native sulphur have been found in connection with it; nor has any salt been found in the waters of the region. These substances are common in association with other gypsum deposits, and are regarded by some persons as indicative of the method of or resulting from their origin as such. Throughout the whole region, the Fort Dodge gypsum has the exact appearance of a sedimentary deposit. It is arranged in layers like the regular layers of limestone, and the whole mass, from top to bottom, is traced with fine horizontal laminæ of alternating white and gray gypsum, parallel with the bedding surface of the layers, but the whole so intimately blended as to form a solid mass. The darker lines contain almost all the impurity there is in th gypsum, and that impurity is evidently sedimentary in its character. From these facts, and also from the further one that no trace of fossil remains has been detected in the gypsum, it seems not unreasonable to entertain the opinion that the gypsum of Fort Dodge originated as a chemical precipitation in comparatively still waters, which were saturated with sulphate of lime and destitute of life; its stratification and impurities being deposited at the same time as clayey impurities which had been held suspended in the same waters.

Much has already been said of the physical properties or character of this gypsum, but as it is so different in some respects from that of other deposits, there are yet other matters worthy of mention in connection with those. According to the results of a complete and exhaustive analysis by Prof. Emery, the ordinary gray gypsum contains only about eight per cent. of impurity; and it is possible that the average impurity for the whole deposit will not exceed that proportion, so uniform in quality is it from top to bottom, and from one end of the region to the other.

When it is remembered that plaster for agricultural purposes is sometimes prepared from gypsum that contains as much as thirty per cent. of impurity, it will be seen that ours is a very superior article for such purposes. The impurities are also of such a character that they do not in anyway interfere with its value for use in the arts. Although the gypsum rock has a gray color it becomes quite white by grinding, and still whiter by the calcining process necessary in the preparation of plaster of Paris. These tests have all been practically made in the rooms of the Geological Survey, and the quality of the plaster of Paris still further tested by actual use and experiment. No hesitation, therefore, is felt in stating that the Fort Dodge gypsum is of as good a quality as any in the country, even for the finest use.

In view of the bounteousness of the primitive fertility of our Iowa soils, many persons forget that a time may come when Nature

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will refuse to respond so generously to our demand as she does now, without an adequate return. Such are apt to say that this vast deposit of gypsum is valueless to our commonwealth, except to the small extent that it may be used in the arts. This is undoubtedly a short-sighted view of the subject, for the time is even now rapidly passing away when a man may purchase a new farm for less money than he can re-fertilize and restore the partially wasted primitive fertility of the one he now occupies. There are farms even now in a large part of the older settled portions of the State that would be greatly benefited by the proper application of plaster, and such eras will continue to increase until it will be difficult to estimate the value of the deposit of gypsum at Fort Dodge. It should be remembered, also, that the inhabitants of an extent of country adjoining our State more than three times as great as its own area, will find it more convenient to obtain their supplies from Fort Dodge than form any other source.

For want of direct railroad communication between this region and other parts of the State, the only use yet made of the gypsum by the inhabitants is for the purpose of ordinary building stone. It is so compact that it is found to be comparatively unaffected by the frost, and its ordinary situation in walls of houses is such that it is protected from the dissolving action of water, which can at most reach it only from occasional rains, and the effect of these is too slight to be perceived after the lapse of several years.

One of the citizens of Fort Dodge , Hon. John F. Duncombe, built a large, fine residence of it, in 1861, the walls of which appear as unaffected by the exposure and as beautiful as they were when first erected. It has been so long and successfully used for building stone by the inhabitants that they now prefer it to the limestone of good quality, which also exists in the immediate vicinity. This preference is due to the cheapness of the gypsum, as compared with the stone. The cheapness of the former is largely due to the facility with which it is quarried and wrought. Several other houses have been constructed of it in Fort Dodge, including the depot building of the Dubuque & Sioux City Railroad. The company have also constructed a large culvert of the same material to span a creek near the town, limestone only being used for the lower courses, which come in contact with the water. It is a fine arch, each stone of gypsum being nicely hewn, and it will doubtless prove a very durable one. Many of the sidewalks in the town are made of the slabs or flags or gypsum which occur in some of the quarries in the form of thin layers. They are more durable that their softness would lead one to suppose. They also possess and advantage over stone in not becoming slippery when worn.

The method adopted in quarrying and dressing the blocks of gypsum is peculiar, and quite unlike that adopted in similar treatment of ordinary stone. Taking a stout auger-bit of an ordinary

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brace, such as is used by carpenters, and filing the cutting parts of it into a peculiar form, the quarryman bores his holes into the gypsum quarry for blasting, in the same manner and with as great facility as a carpenter would bore hard wood. The pieces being loosened by blasting, they are broken up with sledges into convenient sizes, or hewn into the desired shape by means of hatchets or ordinary chopping axes, or cut by means of ordinary wood-saws. So little grit does the gypsum contain that these tools, made for working wood, are found to be better adapted for working the former substance than those tools are which are universally used for working stone.

MINOR DEPOSITS OF SULPHATE OF LIME

Besides the great gypsum deposit of Fort Dodge, sulphate of lime in the various forms of fibrous gypsum, selenite, and small, amorphous masses, has also been discovered in various formations in different parts of the State, including the coal-measure shales near Fort Dodge, where it exists in small quantities quite independently of the great gypsum deposit there. The quantity of gypsum in these minor deposits is always too small to be of any practical value, and frequently minute. They usually occur in shales and shaly clays associated with strata that contain more or less sulphuret of iron (iron pyrites). Gypsum has thus been detected in the coal measures, the St. Louis limestone, the cretaceous strata, and also in the lead caves of Dubuque. In most of these cases it is evidently the result of double decomposition of iron pyrites and carbonate of lime, previously existing there; in which cases the gypsum is of course not an original deposit as the great one at Fort Dodge is supposed to be.

The existence of these comparatively minute quantities of gypsum in the shales of the coal measures and the subcarboniferous limestone which are exposed within the region of and occupy a stratigraphical position beneath the great gypsum deposits, suggest the possibility that the former may have originated as a precipitate from percolating waters, holding gypsum n solution which they had derived from that deposit in passing over or through it. Since, however, the same substance is found in similar small quantities and under similar small quantitites and under similar conditions in regions where they could have had no possible connection with that deposit, it is believed that none of those mentioned have necessarily originated from it, not even those that are found in close proximity to it.

The gypsum found in the lead caves is usually in the form of efflorescent fibers, and is always in small quantity. In the lower coal-measure shale near Fort Dodge, a small mass was found in the form of an intercolated layer, which had a distinct fibrous structure, the fibers being perpendicular to the plane of the layer. The same mass had also distinct, horizontal planes of cleavage at right angles with the perpendicular fibers. Thus, being more or less

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transparent, the mass combined the characters of both fibrous gypsum and selenite. No anhydrous sulphate of lime (anhydrite) has been found in connection with the great gypsum deposit, nor elsewhere in Iowa, so far as yet known.

SULPHATE OF STRONTIA

(Celestine)

The only locality at which this interesting mineral has yet been found in Iowa, or, so far as is known, in the great valley of the Mississippi, is at Fort Dodge. It occurs there in very small quantity in both the shales of the lower coal measures and in the clays that overlie the gypsum deposit, and which are regarded as of the same age with it. The first is just below the city, near Rees' coal bank, and occurs as a layer intercolated among the coal measure shales, amounting in quantity to only a few hundred pounds' weight. The mineral is fibrous and crystaline, the fibers being perpendicular to the plane of the layer. Breaking also with more or less distinct horizontal planes of cleavage, it resembles, in physical character, the layer of fibro-crystaline gypsum before mentioned. Its color is light blue, is transparent and shows crystaline facets upon both the upper and under surfaces of the layer; those of the upper surface being smallest and most numerous. It breaks up readily into small masses along the lines of the perpendicular fibers or columns. The layer is probably not more than a rod in extent in any direction and about three inches in maximum thickness. Apparent lines of stratification occur in it, corresponding with those of the shales which imbed it.

The other deposit was still smaller in amount, and occurred as a mass of crystals imbedded in the clays that overlie the gypsum at Cummins' quarry in the valley of Soldier Creek. Here the mineral is nearly without color, and were it not for the form of the separate crystals would closely resemble a mass of impure chloride. These crystals are so closely aggregated that they enclose but little impurity in the mass, but in nearly every case brought to my notice their fundamental forms are obscured. The mineral of itself is of no practical value, and its occurrence is only interesting as a mineralogical fact.

Epsomite, or native epsom salts, having been discovered near Burlington, we have thus recognized in Iowa all sulphates of the alkaline earths of noatural origin; all of them, except the sulphate of lime, being in a very small quantity. Even if the sulphate of magnesia were produced in nature, in large quantities, it is so very soluble that it can acculmulate only in such positions as afford it complete shelter from the rains or running water. The epsomite mentioned was found beneath the overhanging cliff of Burlington limestone, near Starr's mill.

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It occurs in the form of efflorescent encrustations upon the surface of stones and in similar small fragile masses among the fine debris that has fallen down beneath the overhanging cliff. The projection of the cliff over the perpendicular face of the strata beneath amounts to near twenty feet at the point where epsomite was found. Consequently the rains never reach far beneath it from any quarter. The rock upon which the epsomite accumulates is an impure limestone, containing also some carbonate of magnesia, together with a small proportion of iron pyrites in a finely divided condition. It is doubtless by double decomposition of these that the epsomite results. By experiments with this native salt in the office of the Survey, a fine article of epsom salts was produced, but the quantity that might be annually obtained there would amount to only a few pounds, and of course is of no practical value whatever, on account of its cheapness in the market.

Woodbury County

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