GEOLOGICAL SCALE AND STRUCTURE. 33- 



large bodies of the rock is their small and uniform size. The larger 

 pebbles are generally flat. There is, however, a good deal of variation 

 in all these respects. Much of the conglomerate is fairly even in its 

 bedding and otherwise adapted to quarry purposes. Theformation yields 

 in central and southern Ohio quite a large amount of valuable building 

 and bridge stone. 



The conglomerate is peculiar in this respect, viz., that it is fossilifer- 

 ous, containing both animal and vegetable fossils. The usual Sub-car- 

 boniferous types of both divisions are found in it. It is interrupted by 

 layers of fine or medium-grained sandstone and sometimes by shale 

 deposits. In central Ohio, there are two fairly persistent beds of con- 

 glomerate, as recently shown by Herrick, that can be used in stratigraphi- 

 cal determinations. In a succeeding chapter of this report the divisions 

 that are recognized by the author last named and that are based upon 

 both lithological and paleontological characteristics will be found suc- 

 cinctlyand clearly described. The work of Professor Herrick in this field 

 makes a valuable contribution to our Ohio geology. 



The prevailing colors of the coarse sandstone of the Logan group 

 are j'ellow, red and brown. Some of it is beautifully varigated. Its 

 best developments are in Hocking, Fairfield, Ross, Vinton, Licking, 

 Knox and Wayne counties, which constitute the northwestern arc of the 

 sea-boundary of Ohio in Sub-carboniferous time. South of Ross county 

 it loses most of its pebbles, and south of the Ohio it becomes the Knob- 

 stone formation of Kentuck}'. It is also the Knobstone formation of 

 Indiana, at least in part. In northeastern Ohio the Logan group is 

 also destitute of fossils, and perhaps the conglomerate element proper 

 does not appear here at all. 



White gives a generalized section of the rocks of Erie and Crawford 

 counties of Pennsylvania, in Report Q 4, page 66, of the Second 

 Pennsylvania Survey. He shows the presence of six sandstones in the 

 scale, and three of these are common to the Ohio scale as well. The 

 Shenango sandstone of his column is without doubt the representative 

 of our Logan sandstone and Waverly conglomerate. His Sharpsville 

 sandstone is our Buena Vista stone, and his Corry sandstone appears to 

 be none other than the Berea grit. The sandstones of the Pennsylvania 

 column that underlie the Berea grit do not appear as such in the Ohio 

 scale, as has been already shown. By the same token, White's Orange- 

 ville shale is an equivalent of our Berea shale, his Meadville shales are 

 our Cuyahoga shale in part, and his Shenango shales are a part of our 

 Logan series. 



Interstratified with the conglomerate courses in southern Ohio, are 

 two or more fairly persistent layers of impure limestone. No fossils 

 have been found in them. Similar layers occur in the Logan series of 

 northeastern Ohio, except that in this case the limestones are fossilifer- 



3 G. O. 



