| → 12.5, 1866 1869 |
| 12.5, not only the true coal measures, well known to be here developed in extraordinary force, but likewise the Umbral series, which together compose 1861 |
| 12.5, 1872 |
|
| → of the newer 1866 1869 1872 |
| newer 1861 |
|
| → seen to be much more widely extended, if 1866 1869 |
| greatly increased in size, if we could remove 1861 |
| found much more widely extended than they appear to be, if 1872 |
|
| → were removed which 1866 1869 1872 |
| which 1861 |
|
| → OMIT 1866 1869 1872 |
| at the line of junction have not been metamorphosed, showing that they 1861 |
|
| → OMIT 1869 1872 |
| marking at least sub-stages in the several successive geological epochs, 1861 1866 |
|
|
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
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
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
and granitic rocks exceed, in the proportion of 19 to
→12.5,
the whole
→of the newer
Palæozoic
In many regions the metamorphic and granitic
would be
→seen to be much more widely extended, if
all the sedimentary beds
→were removed which
rest unconformably on them, and which
→OMIT
could not have formed part of the original mantle under which
were crystallized. Hence it is probable that in some parts of the world whole
→OMIT
have been completely denuded, with not a wreck left behind. |
|
| One remark is here worth a passing notice. During periods of elevation the area of the land and of the adjoining shoal parts of the sea will be increased, and new stations will often be formed;— all circumstances
favourable, as previously explained, for the formation of new varieties and species; but during such periods there will generally be a blank in the geological record. On the other hand, during subsidence, the inhabited area and number of inhabitants will decrease (excepting
|
