GEOLOGICAL SCALE AND STRUCTURE. 25 



A calcareous band near the bottom of the series at Bainbridge, Ross 

 county, has yielded a few Hamilton fossils. A band of similiar character 

 near Defiance, and in the same part of the column, yields a few forms in 

 abundance, but not in a very good state of preservation. Newberry re- 

 ports from northern Ohio a number of forms that are counted character 

 istic of the Portage group of New York. 



The great black shale of the mountains of Virginia, which has gen- 

 erally been recognized as of Hamilton age, is the equivalent of the for- 

 mation which we are now describing, and carries some of the same fossils 

 that are alluded to in the preceding paragraph. 



The Erie shale of Newberry, embracing the central and most of the 

 upper portion of the shale column, has yielded a somewhat larger list of 

 fossils at a few points in northern Ohio, from which the age of the beds is 

 shown to be Chemung, a determination of great importance in Ohio geol-' 

 ogy. In higher beds of the same blue shale there are found at a few 

 points forms that are referred to as the Sub-carboniferous. Counting this 

 the boundary line between the Devonian and Sub-carboniferous, Newberry 

 took what he deemed the first identifiable horizon above as the base of the 

 last named division, and accordingly drew the line at the base of the so- 

 called Cleveland shale. This boundary is not a definite one, as subsequent 

 investigations have shown, but the top of the upper black or Cleveland 

 shale would answer fairly well for this purpose. It is the first stratigraphi- 

 cal mark that has any claims to persistency above the beds that hold the 

 fossils already named. The fossils of the black shale proper offer no 

 serious difficulty in the way of extending Devonian time to the upper limit 

 of the stratum, and this boundary is consequently assumed as the only 

 one that can be made practically serviceable. 



The Cleveland shale, limiting the term to the highest bed of black 

 shale in the series, and which is about fifty feet thick at various points 

 near Cleveland, contains a few fossils, most of which are quite small, but 

 the most striking and remarkable fossils at once of the shale formation 

 and of the entire scale of Ohio, remain to be named. They are the great 

 fishes which have been described under several genera and species, by 

 Newberry and later by Claypole. Some of them belong to the basal beds 

 of the black shale, and others, including the largest, are found near the 

 summit. The first of the series were found at the centers of the great 

 concretions that have been already named as characteristic of the forma- 

 tion. The latter are also found in the uppermost beds of the formation 

 in central and southern Ohio, and also in Kentucky, proving the age of 

 the latter to be the same as that of the upper beds of northern Ohio. 



Brief mention must be made of the vegetable fossils of the shales. 

 Fossil wood, derived from trees allied to the pine, is quite common in the 

 lower beds (Huron). The wood is often silicified and the original struc- 

 ture is in such cases admirably preserved. This wood is sometimes found, 

 like the fish remains already noted, at the hearts of the concretions, but 



