191-'.] STEVENSON— THE FORMATION OF COAL BEDS. 517 



of forms occurring in Guernsey and Harrison counties of Ohio, 

 where the rock is a fairly good Hmestone. He found 2 corals, i 

 crinoid, i inarticulated brachiopod, 15 articulated brachiopods, 2 

 pelecypods, 7 gastropods and i cephalopod. Condit in 1909 pub- 

 lished a list from Aleigs county, Ohio, which adds two species of 

 articulated brachiopods. Meek's list from near Morgantown is in 

 contrast with that just given, for it shows one species of inarticu- 

 lated brachiopods, 10 articulated, 12 pelecypods, 7 gastropods, 2 

 cephalopods, to which Stevenson at a later date added one articulated 

 brachiopod, 6 pelecypods and one gastropod. The contrast is due to 

 the fact that the collection, studied by Meek, was made at a locality 

 where the Ames limestone is obscured in a mass of fossiliferous 

 shales extending downward into the horizon of the Pittsburgh reds. 

 At a mile north, the limestone is distinct and has no pelecypods 

 except Myalina and Aznculopecten. In comparing these lists with 

 those from earlier deposits, one finds 23 species in common with the 

 Vanport and 24 with the Mercer. The Ames limestone is succeeded 

 in Pennsylvania by shales, at times 70 to 80 feet thick, in which 

 Raymond found marine forms at several levels. They are not 

 abundant, but 2 species of articulated brachiopods, 6 of pelecypods 

 and one cephalopod were recognized and an Orbiculoidea was found 

 near the top of the deposit at 75 miles east from Pittsburgh. 



It would seem that distribution of the organic types depends 

 often upon the character of the rock. Miss j\Iack observed that 

 pelecypods are more abundant in the shaly layers and brachiopods 

 are more abundant in the purer limestone. Raymond's lists indicate 

 that brachiopods are very numerous in his Vanport localities, where 

 the limestone is good ; it may be that, where White obtained so many 

 pelecypods, the limestone is broken by calcareous shale. The Ames 

 limestone is comparatively pure where Raymond's collections were 

 made and in Ohio it is a good limestone ; pelecypods are very rare 

 — 6 species are recorded but individuals are very few. Near Mor- 

 gantown, West Virginia, the Ames yields no pelecypods except Mya- 

 lina and Aznculopecten, whereas pelecypods and gastropods are abun- 

 dant in the associated shale, the latter, at times, making up the 

 greater part of the mass. Brachiopods are less common in these 



