of level. It has,
however, been suggested by Mr. Hopkins, that if one part of the area,
after rising and before being denuded, subsided, the deposit formed
during the rising movement, though not thick, might afterwards become
protected by fresh accumulations, and thus be preserved for a long
period.

Mr. Hopkins also expresses his belief that sedimentary beds of
considerable horizontal extent have rarely been completely destroyed.
But all geologists, excepting the few who believe that our present
metamorphic schists and plutonic rocks once formed the primordial
nucleus of the globe, will admit that these latter rocks have been
stripped of their covering to an enormous extent. For it is scarcely
possible that such rocks could have been solidified and crystallised
while uncovered; but if the metamorphic action occurred at profound
depths of the ocean, the former protecting mantle of rock may not have
been very thick. Admitting then that gneiss, mica-schist, granite,
diorite, etc., were once necessarily covered up, how can we account for
the naked and extensive areas of such rocks in many parts of the world,
except on the belief that they have subsequently been completely denuded
of all overlying strata? That such extensive areas do exist cannot be
doubted: the granitic region of Parime is described by Humboldt as being
at least nineteen times as large as Switzerland. South of the Amazon,
Boue colours an area composed of rocks of this nature as equal to that
of Spain, France, Italy, part of Germany, and the British Islands, all
conjoined. This region has not been carefully explored, but from the
concurrent testimony of travellers, the granitic area is very large:
thus Von Eschwege gives a detailed section of these rocks, stretching
from Rio de Janeiro for 260 geographical miles inland in a straight
line; and I travelled for 150 miles in another direction, and saw
nothing but granitic rocks. Numerous specimens, collected along the
whole coast, from near Rio de Janeiro to the mouth of the Plata, a
distance of 1,100 geographical miles, were examined by me, and they all
belonged to this class. Inland, along the whole northern bank of the
Plata, I saw, besides modern tertiary beds, only one small patch of
slightly metamorphosed rock, which alone could have formed a part of the
original capping of the granitic series. Turning to a well-known region,
namely, to the United States and Canada, as shown in Professor H.D.
Rogers' bea