GEOLOGICAL SCALE AND STRUCTURE. 21 



The change from the calcareous beds of this age to the next succeed- 

 ing formation is very sharp and well marked, as much so, indeed, as any 

 change in the Ohio scale. 



10. The Ohio Shale. 



(Cleveland Shale, Erie Shale, Huron Shale, of Newberry.) 



A stratum of shales, several hundred feet in thickness, principally 

 black or dark brown in color, containing, especially in its lower portions, 

 a great number of calcareous and ferruginous concretions, many of them 

 large, and all of them remarkably symmetrical, stretches entirely across 

 the state, from the Ohio Valley to the shores of Lake Erie, with an out- 

 crop ranging in breadth between ten and twenty miles. This formation 

 has constituted one of the most conspicuous and well-known features of 

 Ohio geology since this subject first began to be studied. It separates the 

 great limestone series already described, which constitutes the floor of all 

 of western Ohio, from the Berea grit, which is the first persistent sand- 

 stone reached in ascending the geological column of the state, and which, 

 in like manner, may be counted the floor of all of eastern Ohio. By the 

 geologists of the first survey it was designated as the Shale Stratum or the 

 Black Slate. It will be treated in this report under the designation Ohio 

 Shale. Newberry divided it into three divisions, which he named respec- 

 tively the Huron, the Erie and the Cleveland shale. He based the 

 separation of the hitherto undivided mass in part upon the colors of the 

 proposed divisions, the Cleveland and the Huron being counted black 

 shales, and the Erie a greenish-blue shale. The names Huron and Erie 

 were unfortunately chosen, for both are liable to be confounded with cur- 

 rent names of other geological formations. The name Huron was adopted 

 from Alexander Winchell, but a very different range was assigned to it 

 from that which its author originally claimed. Winchell's " Huron 

 group " extends, in his own words, from the top of the Devonian lime- 

 stones, " to the conglomerate above the grit stones of Huron county." 

 It is thus seen to include Newberry's Huron, Erie, Cleveland and Bed- 

 ford shales, together with the Berea grit and Cuyahoga shale. It would 

 have served the interests of geological classification much better to have 

 replaced the term altogether than to have thus restricted it to a small 

 fraction of what it was originally made to cover. The name is also likely 

 to be confounded with the Huronian slates, an older and well established 

 division of the Canadian system of rocks. 



The Erie shale, in like manner, is sure to be confounded with the 

 Erie clay of the Canada Survey, a name given to an important line of 

 deposits of the Glacial period. Both the shale and the clay have their 

 typical exposures in the same localities and their outcrops are not 

 dissimilar in appearance. It is not, therefore, surprising that the names 

 should be confused in popular use. 



