402 J. E. Hyde — Desiccation Conglomerates. 



should show this to be a distinct type of conglomerate of suffi- 

 cient importance to warrant its being placed in a class by itself, 

 the name desiccation conglomerate will be a suitable one. 



The Ames limestone lying near the middle of the Mononga- 

 hela formation and from 150 to 200 feet below the Pittsburg 

 coal is the highest of the marine formations in the Pennsyl- 

 vanian series or Coal-measures of Ohio. Below it there are 

 numerous limestones and chert beds or in some instances shale 

 zones which carry marine faunas, but all of them are thin, 

 although they may occur persistently over wide areas. The same 

 is true of the Ames, which occurs at almost all points in the state 

 where it is due, either on the outcrop or under cover, and is 

 seldom more than three feet thick. Aside from these thin 

 beds and the coal seams, this portion of the Coal-measures series 

 is made up almost entirely of sandstones and argillaceous or 

 sandy shales. The limestones constitute only a small fraction 

 of the total thickness and are mostly of marine origin, the 

 method of deposition of a few being unknown. 



Above the Ames limestone another type of deposit makes 

 its appearance for the first time as an important constituent of 

 the series, the "fresh-water" limestones. In the interval be- 

 tween the Ames and the Pittsburg coal, shales and sandstones 

 like those lying below the former occur throughout the state, 

 but there also occurs here and there a thin stratum of limestone 

 from a few inches to one or two feet thick and often traceable 

 over several square miles with little or no variation. The hori- 

 zon may be represented by a single bed or by two or three thin 

 layers, in which case the separate layers occur as such with 

 greater or less persistency. In general, these limestones become 

 more numerous in passing upward, until in some cases the 25 

 or 30 feet or more of strata immediately below the Pittsburg 

 coal consist of an almost solid bed of limestone. There is great 

 variation in the succession, however, for within a few miles of 

 such a section the Pittsburg seam may be underlain by 40 or 

 50 feet of massive coarse sandstone. 



The Meigs Creek Coal horizon occurs with little variation 

 about 90 or 100 feet above the Pittsburg seam and it is in this 

 interval that the limestones are most conspicuous. In some 

 sections, notably those of Belmont county, with the exception 

 of one to three thin coal beds, the occasional occurrence of a 

 sandstone several feet thick and minor beds of argillaceous 

 shale, the section is practically composed of these limestones 

 and calcareous shales, but in the southern part of the state along 

 the line of outcrop they are replaced by a massive sandstone. 

 In some sections on the extreme western outcrop, the limestones 

 disappear to a noticeable extent and are replaced by shales. 

 Up to 50 feet or more above the Meigs Creek Coal, the lime- 

 stones are usually the predominant feature of the section, but 



