A GEOLOGICAL SKETCH OF WYOMING COUNTY.
By A. P. Chapin.
THIS county presents many interesting features to the geological student, only a few of which can be included in this chapter. Standard works on the subject, and careful observation of the rock formations and water marks as found in the ravines and on the hillsides, will afford ample opportunity to those who desire to pursue the study further than will interest the general reader.
In their lithological character the rocks of this region are much varied in composition and texture. To this fact is due not only those pleasing and beneficial inequalities of surface, but also the origin of some of the streams and waterfalls which beautify and enliven the scenery and encourage agriculture, industry and enterprise among the people. To the same cause to which we owe these prominent features is due also the deep fertile soil prevailing throughout the greater part of the county. The materials excavated from* these valleys, in the form of decomposed and disintegrated rocks, have been transported and reduced to the condition of sand, clay and pebbles, which are distributed over the surface of the lower lands. The high hills and deep valleys and gorges indicate the extent of this work. The effects of erosion are seen, first in the imprint of the falling rain drop - a trifling matter to the ordinary observer, but not so to the geologist; for it remains among the earliest as well as the latest strata, and shows that it rained then as now. It teaches what lands at that time were exposed, and what were buried beneath the waters of the ocean. The gathering drops from the rills combine into rivulets, and the rivulets wear pathways down the hillsides. The rivulets unite to form larger streams, and these work with accumulating force and excavate deep gorges. The mist and rains about the higher lands are usually the main source of the water. As the streamlets combine the torrent increases, and thus exercises the greatest force near the base of the declivity. There the valley first takes its shape and size. Examples of this form of erosion may be found among the tributaries of Allan's creek, and in various other parts of the county. As the erosion continues a constantly deepening valley is formed, the head of which slowly but surely travels up the stream. The nature of the rocks causes modifications in these results. If the rocks are of a soft shaly character, as are many of the rocks in this region, the work progresses much more rapidly than among rocks of a dense and compact character. The composition of the rocks may also have much to do in regulating the rate of wear. Many examples are on record where gorges hundreds of feet deep have been cut in the solid rock by the work of only two or three centuries. This, however, is accomplished only under the most favorable circumstances. Although the rocks of Wyoming county are not of the denser varieties, doubtless her precipitous valleys have been undergoing many centuries of formation. The products of erosion are carried down into the valleys, where the speed of the water slackens, and there form the alluvial beds so characteristic of the valleys.
The soil of the entire county rests upon rocks known as the
This group presents an extensive development of shales and flagstones, and some sandstone toward its upper part. It is extremely variable in character at different points. " From its superior development along the banks of the Genesee river in the vicinity of Portage it has received that name to distinguish it from the higher rocks, which possess some differences in lithological characters, but a more striking dissimilarity in organic remains." This group rises sometimes in a gentle slope, and at other times quite abruptly from the softer shales below. The enduring sandstones of the upper part have enabled it to withstand the action of air and water to a considerable degree. These sandstone formations often extend well to the northward on the elevated grounds between the deep valleys, running in a north and south direction, or nearly so. The valleys are generally bounded by steep hills, thinly covered with northern drift. This character of the formation is well illustrated along the Genesee valley for several miles below Portage bridge, and in the valleys of Allan's creek and the Tonawanda creek. On approaching the northern margin of the Portage group the observer finds a gradually increasing elevation of hills and abruptness of slope. These elevations often extend several miles unbroken, except partially by the deep ravines which indent their sides, and which originated in water-courses which took their rise upon the summits of these hills.
The higher sandstones of the group, and in many instances the intermediate ones, have produced falls in the streams which pass over them. Some of the most beautiful cascades in the State are found among the rocks of this group. The highest perpendicular fall of water in the State is found in the rocks of this group, and its grand and picturesque scenery is rarely equaled. The traveler often finds his course impeded by a deep gorge, and in the very bottom of this is the small winding stream, the only representative of the once rushing torrent that has worn so deep a pathway through the rocks. The rocks of this group are generally divided into three parts. The lower of these is known as the
This rests upon what is known as the Genesee slate. It differs in its fossils sufficiently from those above to be considered under a separate* name. From its more complete development upon the Cashaqua creek the name was originally applied to it, and before the overlapping rocks had been thoroughly examined. This formation consists of a soft, argillaceous rock of a greenish color, which rapidly crumbles on being exposed to the atmosphere and storms, and forms a soft, sticky clay. It is therefore difficult to procure good specimens, and its fossils, not being abundant, are quite apt to be overlooked. Certain species of shells, however, have been found only in this rock, and these are found in the same position to an extent of one hundred and fifty miles. On tracing it west of the Genesee it presents continually the same features as on the Cashaqua creek. The lower part is occasionally darker colored, and in some places is separated from the Genesee slate by a thin band of a species of limestone. It is largely exposed in the numerous streams and ravines situated in the hills bordering on Allan's creek and Tonawanda creek. It appears at the village of Wyoming and at numerous other points in that vicinity, its greatest thickness" at any visible point is on the Genesee river, and is about one hundred and ten feet. It decreases in thickness toward the north, and disappears on a line running through the southern part of Genesee county. Resting upon this is the middle division of the Portage group, known as the
Gardeau Shale and Flagstones.
Along the Genesee river, above the Cashaqua shale, we find an extensive development of greenish black slaty and sandy shales, of various shades of color between green and black, with thin layers of sandstone, which form beautiful and enduring flagstones. These flagstones are found in the same geological position in several places in this county, and adorn many of the streets of our villages. These rocks form high, almost perpendicular banks on the Genesee and in some of the numerous ravines of this county, only indented as the results of slides or running water. From their extensive exposure along the Gardeau reservation that name was adopted to distinguish this part of the formation. As we ascend the arenaceous matter increases, and the shale forms distinct alternations of black and green, often many times in succession within a perpendicular distance of fifty or sixty feet. The sandstone layers in the upper part of the formation are generally too thick for flagstones, and the shale divides into thicker leaves. These characteristics, however, vary considerably in different localities, and the observer needs to note carefully the composition of the rocks and the few native fossils, to be sure of his position.
"The thick-bedded sandstones at Portage form the terminal rocks of the group. These are well exposed in the deep gorge below Portageville, where the perpendicular cliffs rise to the height of three hundred and fifty feet. The upper part consists of thick-bedded sandstone, with little shale; while below the sandy layers become thinner, with more frequent alternations of shale. The character of the sandstones, and the presence of fucoids passing vertically through the strata, induced the separation from the rocks below, where the characteristic species of the same genus lies horizontally upon the surface of the strata. The lithological character of the sandstone, and the presence of the vertical fucoid, hold uniform over a considerable extent; and the presence of the latter alone is often sufficient to decide the position of the rock where it is but slightly exposed."
The preceding description of these three divisions will furnish a correct idea of the group, and will apply to nearly if not quite the entire surface of Wyoming county. The whole series consists of shales and shaly sandstones. Nevertheless, in lithological characters there is no abrupt change, or evidence of very different conditions in the ocean from which they were deposited, from the termination of the Tully limestone to the final deposition of the Chemung group. Shales and sandstones compose the entire assemblage. The Portage group forms the lower part of this great division of rocks.
Throughout the entire thickness of the Portage group, which is not less than one thousand feet, there are but two forms of organic remains, which can be referred to the Brachiopoda; one of these is the Delthyris, and the other the Orthis. Both of these are quite unlike any others which have been seen in the rocks above or below. Shells of this family, though of a different variety, predominate in the Hamilton and Chemung groups, and are much more numerous than .in the Portage group. In addition we find the Goniatites, a group of Cephalopods with Nautilus-like shells; the Bellerophon, a genus of Heteropods, with the respiratory and digestive organs forming a kind of nucleus on the posterior part of the back, and with the foot divided into a ventral fin, sucker and terminal fin. They are rapid swimmers, found at the surface in mid-ocean, moving by their fin-shaped foot and tail, and attaching themselves to seaweed by the sucker. They feed on minute pteropods and jelly fishes. These are the animals which lived in the great ocean of waters while all this region was beneath its surface, and while its slow but constant deposition formed the rocks covering a large portion of western New York. The paucity of fossils in this group, when compared with those below and above it, is a marked characteristic. Whole days maybe spent without finding more than a few, and some times even no shells. In a few localities some forms have been detected which seem peculiarly typical of the group, and so far as at present known, have never been found elsewhere.
In. this absence of fossil shells we find a great abundance of marine vegetation, or fucoids. Scarcely a locality can be examined where one or more species does not occur. The Fucoides Graphica occurs in great numbers, in short, rigid fragments, throughout the central portion of the group, and generally lying on the surface of the thin layers of flagstones. The sidewalks often furnish good specimens of this class of fucoids. They are also often found in profusion in the beds of the ravines, having fallen down in broken fragments of rocks from either side. The Fucoides Verticalis is characteristic of the upper part of the group. It may be at the lower falls of Portage, and in many of the sandstone strata above this; but it is most abundant in the upper sandstone at Portage. The terminating mass of the group may be everywhere recognized by its presence. These constitute the principal fossils of this group of rocks, and they are the only ones that occur with any regularity in this county, though some few others may be occasionally found.
Ripple marks are abundant in the sandy shale, or where the shale becomes interstratified with sandstone; but it is often difficult to obtain good specimens. Many of them have the appearance of being produced by a "chopped sea," or where a current opposed the direction of the wind. The same effect is often visible on sandy beaches where the tide has ebbed; the surface being broken, interrupted and irregular ripples produced either by the tidal current opposing the wind or by some other similar conflict of forces. There is abundant proof among the strata that such circumstances were in operation at the time these rocks were deposited, and that the sea was alternately shallow and again deeper. The dark and green shales bear no evidence of ripple marks, or diagonal lamination, and were probably deposited in deep water; but all the sandy shales and alternations of shale and sandstone furnish evidence of a shallow sea.
"This group throughout presents a great variety of concretionary forms. The strata, however, are all uniform, and rarely give any appearance of concretionary structure in themselves. The concretions are more or less calcareous in different parts of the group and in different shales. The more perfectly spherical, with seams of crystalline matter, are found in the black shale, while the forms varying from this to the very flat or lenticular ones are found in the shales varying from blackish to greenish black and green." The more spherical forms are due to a higher degree of crystallization, which results from a larger proportion of carbonate of lime, while the flattened forms are less crystalline, and consequently less spherical, from the larger amount of argillaceous matter. These forms are too well known to need further description. They sometimes assume fantastic shapes, which cause them to be mistaken for organic bodies. This arises from the seams on the surface, which are fancied to resemble the lines of suture in the shells of the tortoise or turtle, and by these names they are frequently known in localities where they occur plentifully. The more usual form of these bodies is that of a flattened spheroid. They are in some places burned for hydraulic cement, and produce a very good material for this purpose.
The minerals of the Portage group of rocks are as follows, and all are represented in Wyoming county: The concretions contain crystallized carbonate of lime, and sometimes sulphate of baryta. Iron pyrites is freely disseminated through the rock, and from its decomposition the surface of the slaty laminae and the sides of joints are often stained with iron. It also gives origin to sulphate of lime, or gypsum, which often coats the shaly laminae, or appears in the form of small crystals in the seams and joints. Carbonaceous matter is disseminated through the black shales, and sometimes appears in seams of half an inch in thickness. Some fragments of large vegetable forms appear, and thin laminae of coal usually accompany these. From the frequency of these small seams of coal, which are usually of no greater extent than the specimen procured, excavations and borings have been made, in the hope of finding large deposits of coal. It ought to be unnecessary to say that these undertakings in rocks of this period always have failed, and always will fail. If the people could be made to understand that coal does not exist in any valuable quantity in these rocks, useless expenditure of time and money might be prevented. They seem, however, to prefer to learn the lesson at the cost of their own experience in a vain effort to find it.
Springs and Soils.
Numerous never failing springs water well this region of country. Except where the black slaty shale is thick there is no difficulty in procuring water. In these shales the vertical joints seem to be more open and to allow the water to percolate through them. The only remedy for this is to bore through the black to the green shales, which are more impervious to water. In the present condition of this county there is little difficulty in procuring the desired supply with slight labor and expense. If the true origin of springs was generally known, and means taken to protect them, the supply of water would always be plentiful. If, however, the higher lands should be robbed of their shady woods, many of the springs and smaller streams will disappear.
The soil in the northern part of the county is generally a stiff clay, the sand being in too small proportions to produce much perceptible effect. Farther south the arenaceous matter increases, and the broken fragments of the sandy strata become intermixed with the finer materials, giving it the character of a clayey gravel. The valleys and the lower northern slopes are more deeply covered with northern drift and alluvium, and the soil contains a larger proportion of calcareous matter. This calcareous matter is composed chiefly of decomposed limestone and calcareous shales, with a small admixture of sand. This kind of soil is but sparingly spread over the hilltops, and in some of the highest localities is scarcely seen at all. In consequence of this the character and productions of the soil of the bills and valleys are quite different
In the valleys and on the low northern slopes the soil produces wheat with the same facility as the soil of the formations which come to the surface immediately to the north of the Portage group. As we ascend to the south the wheat crops are less abundant and less certain, and give place largely to the coarser grains and to pasturage. For the latter purpose the soil is superior to that on the north of it, and this fact is fully substantiated by the increasing number of cattle and the product of the dairies.
SOURCE: History of Wyoming County, N.Y., with Illustrations, Biographical Sketches and Portraits of Some Pioneers and Prominent Residents; F. W. Beers & Co.; 1860