Origin of Species Variorum

Comparison with 1872

the whole of the newer Palæozoic formations. In many regions the metamorphic and granitic rocks would be found much more widely extended than they appear to be, if all the sedimentary beds were removed which rest unconformably on them, and which ... could not have formed part of the original mantle under which they .. were crystallized. Hence it is probable that in some parts of the world whole formations ... 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 most 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 .. on the shores of a continent when first broken up into an archipelago), and consequently during subsidence, though there will be much extinction, fewer new varieties or species will be formed; and it is during these very periods of subsidence, that the deposits which are richest in fossils have been accumulated. ↑

On the Absence of Numerous Intermediate Varieties in any one Single Formation .

From the foregoing considerations, it cannot be doubted that the geological record, viewed as a whole, is extremely imperfect; but if we confine our attention to any one formation, it becomes more difficult to

the whole newer Palæozoic formation. In many regions the metamorphic and granitic areas would be greatly increased in size, if we could remove all the sedimentary beds which rest unconformably on them, and which at the line of junction have not been metamorphosed, showing that they could not have formed part of the original mantle under which the granitic rocks were crystallized. Hence it is probable that in some parts of the world whole formations, marking at least sub-stages in the several successive geological epochs, 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 the productions on the shores of a continent when first broken up into an archipelago), and consequently during subsidence, though there will be much extinction, few new varieties or species will be formed; and it is during these very periods of subsidence, that our great deposits rich in fossils have been accumulated. Nature may almost be said to have guarded against the frequent discovery of her fine transitional or linking forms. ↑

From these several considerations it cannot be doubted that the geological record, viewed as a whole, is extremely imperfect; but if we confine our attention to any one formation, it becomes much more difficult to