J. E. Hyde — Desiccation Conglomerates. 403 



above this they are of less importance and occur as scattered 

 beds in a mass of shale which in the southern part of the state 

 is also largely replaced by sandstones. 



It is difficult to characterize in a few words so variable a 

 series as this, but the above remarks will serve to show the 

 general method of occurrence of the limestones, which lie in 

 extensive basins and accumulated to a thickness of 100 or 150 

 feet or more. During the period of deposition it is quite evident 

 that there were numerous interruptions of the process of sedi- 

 mentation, as is shown by the presence of from two to five coal 

 seams varying from one to six feet in thickness, and sandstones 

 locally as much as 25 or 50 feet thick, as well as occasional beds 

 of argillaceous shale. 



The litholoodcal and chemical character of the limestone 

 varies widely. They are usually magnesian and have a high 

 percentage of silica and sometimes of clayey material. They 

 vary from hard ringing layers which resist the weather well to 

 limestones which weather up into small sharp conchoidal frag- 

 ments on exposure of a few weeks. All gradations occur 

 between limestone and moderately soft calcareous shale. The 

 limestones are amorphous and bine to gray or brownish in 

 color. Individual layers in places maintain their characteristics 

 over considerable areas, but again they may change rapidly over 

 distances of a mile or two. Contrary to the prevalent idea, 

 these limestones are quite fossiliferons, and it is seldom that a 

 search of a few moments is not rewarded by many small indi- 

 viduals. The fauna is limited to probably not more than four 

 or five species, all minute, the most abundant being small 

 ostracod carapaces which cover some of the bedding planes, 

 notably on mud-cracked surfaces, by the hundreds. Spirorbis 

 anthracosia Whitf . is numerous. In certain layers, especially 

 near the top of the limestones at a horizon not far below the 

 Waynesburg coal, small gastropods are very abundant, among 

 them a form either identical with or very similar to Anthra- 

 copujpa ohioensis Whitf. Mud-cracked surfaces are not uncom- 

 monly seen on loose slabs in stream beds or cuttings, and 

 are doubtless much more abundant than can be gathered from 

 a study of the cliff-like exposures, which are usually the only 

 ones available. Layers of conglomerate, consisting of frag- 

 ments of limestone cemented in a limestone matrix, occur 

 throughout the series. Their thickness ma}^ vary from a 

 fraction of an inch to two or three feet. The fragments are 

 usually small, from the size of a pea or less up to an inch or 

 two in diameter and rarely four or six inches in diameter. These 

 layers differ in their nature, many being undoubtedly formed 

 in the manner just described, but others which are thicker have 

 the appearance of a true breccia in which the angular frag- 

 ments have been cemented in a matrix of argillaceous lime- 

 stone, the fragments being larger and bearing no apparent 



