392 Review of the Progress of 
in nature can yield on the application of asufficient force —(Gla- - 
ciers of the Alps, p. 404, Amer. Kd.) 
Though these specimens are not so definitely described as we 
could wish, we presume they are conglomerates with flattened 
quartz pebbles, like those in Rhode Island and Vermont. Our 
objections to Prof. Tyndall’s hypothesis, which imputes the effect 
wholly to the mechanical compression of solid quartz, are as 
follows: 
1. The compression of pure quartz pebbles, such as some of 
those in Rhode Island, and most of those in Vermont, would 
break and crush them, nor have we any reason to suppose that 
the fragments could be reconstructed so as to form hyaline 
masses, without fissures. There is no fluid, as in ice, to produce 
regelation; nor could the particles be brought near enough for 
molecular attraction, without being crushed into the finest pow- 
der, by such a pressure as the facts show not to have been ex- 
erted upon the conglomerates. 
2. The compressing force has not been great enough to de- 
OY except partially, the form of the pebbles. It has not 
crushed but only moulded them, except that now and then, one 
has been fractured, If it had been powerful enough to compress 
and distort solid quartz and to reunite its particles, it must have 
destroyed all marks of a mechanical origin in the pebbles 
: ‘here is evidence, as we have tried to show, in the prece- 
ding discussion, that many of the pebbles, especially in the Ver- 
mont rocks, have undergone a chemical change; that certain 
silicates have been abstracted from them, leaving the excess of 
Silica in the form of quartz. This, of course, would require 
such a degree of plasticity, as to enable water to permeate the 
ass 
March 20th, 1861. 
Art. XXXV.—On some points in American Geology; by T. 
Srerry Hunt, F.R.S., of the Geological Survey of Canada. 
THE reeent publication of two important volumes on Ameri- 
can geology seems to afford a fitting occasion for reviewing some 
questions connected with the progress of geological seience, and 
with the history of the older rock formations of North America. 
The first of these works is the third volume of the Paleontology 
of New York by James Hall; we shall not attempt the task of 
noticing the continuation of this author's labors in the study of 
organic remains, labors which have by common consent plac 
him at the head of Ameriean paleontologists, but we have to 
attention to the introduction to this third volume, where 10 
about a hundred pages Mr. Hall gives us a clear and admirable 
