32 



GEOLOGY OF OHIO. 



Second. That the grooving, polishing, fluting, and carving of th? 

 rocks is precisely that done by glaciers, and such as could not be pro- 

 duced by floating ice. 



Third. The bowlder clay which covers so much of the glaciated sur- 

 face is generally unsiraiified, and hence could not have been deposited 

 from water, and it everywhere contains angular or imperfectly rounded 

 fragments of rocks, frequently brought from neighboring localities and 

 lower levels, planed and striated, as glacier- worn pebbles always, and as 

 water-worn pebbles never, are. 



Fourth. The objection that there was no declivity down which gla- 

 ciers could descend on to Ohio, has been considered by Dana,* by the 

 ■writer,t and others; and it has been shown that from the practical 

 plasticity of ice, if it were to accumulate to the thickness of several thou- 

 sand feet on the Canadian highlands, and was prevented from moving 

 borthward by an unyielding ice barrier, it would fljw off to the south, 

 over any minor topographical irregularities, until it reached a point 

 where it was melted by a warmer climate. It may also be said that 

 even if it were impossible to explain how glaciers could have reached 

 Ohio, the fact that they have been here is attested by the deeply graven 

 and unmistakable record they have left. 



THE ERIE CLAY. 



This, the first and lowest member of our Drift series, is fully described 

 in the second volume of this report, but its nature and origin do not 

 seem to have been clearly understood by all those who have since refer- 

 red to it. The name Erie clay was first used by Sir Wm. Logan, and 

 applied to the lowest Drift clay, on the north side of Lake Erie, the 

 exact equivalent of the clay which holds the same position in Ohio. It 

 corresponds to the Till or Bowlder clay, which covers so much of the rock 

 surface glaciated in the ice period in the British Inlands, and to the 

 grunde-mordne and moraine profonde of the geologists of Germany, France, 

 and Switzerland. 



6 In the description of the Erie clay contained in Chapter XXX, the 

 laminated clay which locally overlies the true Bowlder clay, was united 

 with it, on the supposition that this was deposited in local water basins 

 synchronously with some portion of the sheet which it formed, but in 

 view of facts which have been more recently brought to light, it has 

 seemed best to distinguish the two clays by different names; the lam- 

 inated clay having baen proved to ba fojsiliferous, the product of a s^low 



• Manual, Second Edition, jiajje 5130. 

 t Geology of Oliio, Volame I, page 69. 



