2 « 2 The Poorness of our Chap. x. 



consecutive. But we know, for instance, from Sir R. Murchison's 

 great work 'on Russia, what wide gaps there are in that country 

 between the superimposed formations; so it is in North America, 

 and in many other parts of the world. The most skilful geologist, 

 if his attention had been confined exclusively to these large ter- 

 ritories, would never have suspected that, during the periods which 

 were blank and barren in his own country, great piles of sediment, 

 charged with new and peculiar forms of life, had elsewhere been 

 accumulated. And if, in each separate territory, hardly any idea 

 can be formed of the length of time which has elapsed between the 

 consecutive, formations, we may infer that this could nowhere be 

 ascertained. The frequent and great changes in the mineralogical 

 composition of consecutive formations, generally implying great 

 changes in the geography of the surrounding lands, whence the 

 sediment was derived, accord with the belief of vast intervals of 

 time having elapsed between each formation. 



We can, I think, see why the geological formations of each region 

 are almost invariably intermittent ; that is, have not followed each 

 other in close sequence. Scarcely any fact struck me more when 

 examining many hundred miles of the South American coasts, which 

 have been upraised several hundred feet within the recent period, 

 than the absence of any recent deposits sufficiently extensive to last 

 for even a short geological period. Along the whole west coast, 

 which is inhabited by a peculiar marine fauna, tertiary beds are so 

 poorly developed, that no record of several successive and peculiar 

 marine faunas will probably be preserved to a distant age. A little 

 reflection will explain why, along the rising coast of the western 

 side of South America, no extensive formations with recent or ter- 

 tiary remains can anywhere be found, though the supply of sediment 

 must for ages have been great, from the enormous degradation of 

 the coast-rocks and from muddy streams entering the sea. The 

 explanation, no doubt, is, that the littoral and sub-littoral deposits 

 are continually worn away, as soon as they are brought up by the 

 slow and gradual rising of the land within the grinding action of 

 the coast-waves. 



We may, I think, conclude that sediment must be accumulated 

 in extremely thick, solid, or extensive masses, in order to withstand 

 the incessant action of the waves, when first upraised and during 

 successive oscillations of level, as well as the subsequent subaerial 

 degradation. Such thick and extensive accumulations of sediment 

 may be formed in two ways ; either in profound depths of the sea, 

 in which case the bottom will not be inhabited by so many and 

 such varied forms of life, as the more shallow seas ; and the mass 



