Reviews— Geological Survey of Ohio, 559 



tissue, and are turned up anteriorly like sledge-runners, the extremities 

 of both jaws meeting to form one great triangular tooth, which in- 

 terlocked with two in the upper jaw seven inches in length and more 

 than three inches wide. It is apparent from the structure of these 

 jaws that they could easily embrace in their grasp the body of a 

 man — perhaps a horse ; and as they were doubtless moved by 

 muscles of corresponding power, they could crush such a body as 

 we would crack an egg-shell."^ 



The " Hamilton Group," the next in descending order, which is 

 well developed in Michigan, was heretofore unknown in Ohio. It is 

 a compound mass of limestones and shales. This, with the Erie and 

 Huron shales, corresponds to our Upper Old Red ; whilst the next 

 two, the " Corniferous Limestone" and the " Oriskany Sandstone/' 

 are the supposed equivalents of the Devon and Eifel Limestones. 



Neither these Devonian rocks nor the Silurians had, up to the 

 dates of the report, been made the subject of such minute study as 

 the formations in the eastern half of the State ; but their general 

 trend is sufficiently indicated. Their distribution is entirely de- 

 pendent on a great anticlinal, the axis of which may roughly be 

 taken as running from near Toledo at the western extremity of Lake 

 Erie to Cincinnati on the Ohio. 



The result of this master-fold, and of the subsequent denudation 

 of its summit, is, that in the south-western corner of the State only do 

 all the members as far down as the Cincinnati group crop out. In 

 the north, both that formation and the " Clinton Group " are buried 

 beneath the arch ; an island of the topmost beds of the Niagara alone 

 is seen in the form of an inlier immediately along the axis. The 

 "Water-lime and Salina Group" surrounds it on three sides and dips 

 away from it to the west and east. Above this the newer beds once 

 more make their appearance one by one, in the north-west corner, 

 viz. the " Oriskany," the " Corniferous," the " Hamilton," and the 

 "Huron" groups, all dipping to the west. 



We have thought it preferable to sketch thus rapidly the geological 

 structure of Ohio as a whole according to the data now afforded us, 

 rather than to dwell on some of the many interesting local details with, 

 which these works abound ; more especially as the latter are still in 

 their rough state, and will no doubt be more fully discussed in the 

 complete final report. Such are for instance the numerous facts as 

 to the divisions of the Drift in Ohio, concerning which we will only 

 say that none of the authors who treat this branch of the subject 

 seem to find any difficulty in following to a great extent Dr. Dana's 

 theory of the origin of the glacial deposits of that region, as against 

 that so staunchly upheld by Principal Dawson. 



One or two facts we must, however, not pass in silence. One is 

 the occurrence in Williams County of two distinct lake beaches, 

 accurately marking contour lines, concerning which more details 

 would be acceptable. The other is, that the old channels now filled 

 with Drift are shown to have been of a much greater depth than 



^ For an account of this Fish, with Woodcut figures, see Geol. Mag., 1868, Vol. 

 v., p. 184. 



