214 
GEOLOGY OF THE FffiST DISTRICT. 
elevation of about one thousand feet above them.* Three of these holes 'were observed within 
a few feet of each other ; two circular, and about three and two feet in diameter, and several 
feet deep; the other, oblong, and of greater diameter. The rock is smooth, and seems to 
have been worn away to a depth of fifteen or twenty feet, over a breadth of forty or fifty feet. 
Among other proofs of this fact, another worn cavity is mentioned, eight or ten feet higher 
than the others, and a little back of the middle one. This cavity is very perfect, and is 
plainly to be seen to the depth of six or seven feet, about three feet in diameter at top, appa¬ 
rently perfectly round, and like other cavities known to be formed by the action of gravel and 
water. Its diameter increases very regularly and gradually as it grows deeper; and that 
which makes it still more certain that it is the effect of gravel and water, is, that about three 
or four feet from the top, the rock on one side of the cavity projects on one side into the hole 
three or four inches, exactly as those rocks do that are known to be worn by gravel and water, 
where a part of the rock is harder than the rest. This is clearly the case here, as that part 
of the rock is of a more compact texture and of a different color.* 
The occurrence of pot-holes at high levels, far above the reach of currents of water flowing 
as they do at present, is conclusive evidence that the level, the quantity, and the velocity of 
water, have, at some former period, been different from what they are at present, at their 
localities ; and their occurrence with smoothed rocks, and near extensive depositions of drift, 
render it highly probable, though not absolutely certain, that they were formed at the epoch 
of the drift deposits. 
THEORIES OF ERRATIC BLOCKS, BOULDERS, SCRATCHES, &c. 
Many theories have been advanced to account for the transported blocks, boulders and 
gravel; the scratches, smoothed surfaces, and the various phenomena connected with the drift 
deposits. Some of them, in their prominent features, and brought into as concise a form as 
practicable, are subjoined. They were framed so as to account in the most plausible manner 
for the facts then known. 
1. That of Deluc, who supposed these blocks had been cast into the air by the force that 
had elevated the mountains, and that they had fallen at a greater or less distance ; according 
to the power of this force and its direction.! 
2. That of MM. De Buch, Escher, &c., who supposed that an immense deluge swept the 
boulders and blocks along, and forced them up the acclivities of the mountains by means of 
the impulse they had received.! 
3. Others have thought that the blocks, pebbles, etc. were the -wrecks of a mantle of rocks 
of similar kinds, which originally covered the surface, and of which these are the only 
remains.! 
* American Journal of Science, Vol. 9, pp. 30, 31. 
t Brongniart. Terrains de I’dcorce du globe. Paris, 1829, pp. 76, 77. 
