280 THE ORIGIN OF SPECIES 



and I travelled for 150 miles in another direction, and saw noth- 

 ing but granitic rocks. Numerous specimens, collected along the 

 whole coast, from near Rio 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's beautiful 

 map, I have estimated the areas by cutting out and weighing the 

 paper, and I find that the metamorphic (excluding the "semi- 

 metamorphic") and granite rocks exceed, in the proportion of 

 19 to 12.5, the whole of the newer Palaeozoic formations. In many 

 regions the metamorphic and granite rocks would be found much 

 more widely extended than they appear to be, if all the sedi- 

 mentary 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 com- 

 pletely 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 favorable, 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, few 

 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 SINGLE FORMATION 



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 understand why we do not therein find 

 closely graduated varieties between the allied species which lived 

 at its commencement and at its close. Several cases are on record 



