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 great distance from the coal fields and the 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 valleys of the smaller streams and 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.

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 land

scape.

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

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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 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 from alternating fine horizontal lines of nearly white, with similar 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 intercalation of 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 than 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, doubtless, 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, particulary in its lower part, it has doubtless served 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 long since 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. An analysis of water from one of these springs will be found in Prof. Emery's report.

Besides the clayey 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.

Age of the Gypsum Deposit.—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 newer 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 is 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, 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 quantities of oxide of iron nor any 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 lamina of alternating white and gray gypsum, parallel with the bedding surfaces 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 the gypsum, and that impurity is evidently sedimentary in its character. Fren 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.

Physical Properties.—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 to 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 any way 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 uses.

In view of the bounteousness of the primitive fertility of our Iowa soils, many persons forget that a time may come when Nature 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 areas 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 from 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 purposes 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 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 of gypsum which occur in some of the quarries in the form of thin layers. They are more durable than their softness would lead one to suppose. They also possess an 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 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 shapes 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 car