32 GEOLOGY OF OHIO. 
Second. That the grooving, polishing, fluting, and carving of the 
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 unstratified, 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 ah 
ciers could descend on to Ohio, has been considered by Dana,*: by the 
writer,j and others; and it has been shown that from the practical 
plasticity of ice, if if were to accumulate to the thickness of several thou- 
sand feet on, the Canadian highlands, and was prevented from moving 
northward by an unyielding ice barrier, it would flow 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 Hrie, 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 Islands, and to the 
grunde-mordne and moraine profonde of the geologists of Germany, France, 
and Switzerland. 
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 bsen proved to be fossiliferous, the product of a slow 
* Manual, Second Edition, page 536. 
t Geology of Ohio, Volume I, page 69. 
