be much consolidated, nor
would it would it 1861 | would it 1866 1869 1872 |
be capped by overlying
formations, so that it would run a good chance of being worn away
during during 1861 |
by atmospheric degradation and by the action of the sea during 1866 1869 1872 |
subsequent oscillations of level. It
has has 1861 | has, 1866 1869 1872 |
been been 1861 | however, been 1866 1869 1872 |
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
become become 1861 | afterwards become 1866 1869 1872 |
protected by fresh accumulations, and thus be preserved for
an extremely long period,— a consideration which I formerly overlooked. an extremely long period,— a consideration which I formerly overlooked. 1861 |
a long period. 1866 1869 1872 |
|
Mr.
Hopkins, Hopkins, 1861 | Hopkins 1866 1869 1872 |
in commenting on this subject, states that he believes the entire destruction of any in commenting on this subject, states that he believes the entire destruction of any 1861 |
also expresses his belief that 1866 1869 1872 |
sedimentary
bed bed 1861 | beds 1866 1869 1872 |
of considerable horizontal extent
to
have
been of rare occurrence. been of rare occurrence. 1861 |
rarely been completely destroyed. 1866 1869 1872 |
↑1 blocks not present in 1859 1860 1861; present in 1866 1869 1872 | 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 probably
admit that rocks of this nature must
have been denuded on
an enormous scale.
|
My remarks apply solely to beds rich in fossils: I have admitted that sediment accumulated in extremely thick, solid, or extensive masses would escape denudation. The point in question is, whether widely extended formations, rich in fossils, and of sufficient thickness to last for a long period, would be formed except during periods of subsidence? My impression is that this has rarely been the case. As the subject of complete denudation has been broached by Mr. Hopkins, I may remark that all geologists, excepting the few who believe that they see in the metamorphic schists and plutonic rocks the heated primordial nucleus of the globe, will probably admit that rocks of this nature must have been largely denuded. For it is scarcely possible that
these these 1861 1866 | such 1869 1872 |
rocks
should should 1861 | could 1866 1869 1872 |
have been solidified and crystallized
in a naked condition; in a naked condition; 1861 |
whilst uncovered; 1866 1869 1872 |
but if the metamorphic action occurred at profound depths of the ocean, the former
mantle mantle 1861 |
protecting mantle 1866 |
protecting mantle of rock 1869 1872 |
may not have been
thick. thick. 1861 | very thick. 1866 1869 1872 |
Admitting then that
such rocks as such rocks as 1861 1866 |
OMIT 1869 1872 |
gneiss, mica-schist, granite, diorite,
&c, &c, 1861 | &c., 1866 1869 1872 |
were once necessarily covered up, how can we account for the
extensive extensive 1861 | naked 1866 1869 1872 |
and
naked naked 1861 | extensive 1866 1869 1872 |
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: doubted: 1861 1866 1869 | doubted; 1872 |
the granitic region of Parime is described by Humboldt as being at least nineteen times as large as Switzerland. South of the
Amazon Amazon 1861 | Amazon, 1866 1869 1872 |
Boué colours an area composed of
such such 1861 | such 1866 1869 1872 |
rocks
as as 1861 |
of this nature as 1866 1869 1872 |
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
must be must be 1861 1866 | is 1869 1872 |
very
large: large: 1861 1866 1869 | large; 1872 |
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 direction 1861 1866 | direction, 1869 1872 |
and saw nothing but granitic rocks. Numerous specimens, collected along the whole coast from near Rio Janeiro to the mouth of the Plata, a distance of 1100 geographical miles, were
shown shown 1861 | examined by 1866 1869 1872 |
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's beautiful map, I have estimated the areas by cutting out and weighing the paper, and I find that the metamorphic (excluding
"the "the 1861 | "the 1866 1869 1872 |
semi-metamorphic") semi-metamorphic") 1861 | semi-metamorphic") 1866 1869 1872 |
|