! 



to 



to 



.s 



of 

 id 



in 



■ 



Ch. XII.] 



FORMER GEOGRAPHICAL CHANGES. 



2K K 

 55 



The great slowness with which the change is always brought 

 about results from a peculiarity in the external configuration 

 of the earth's crust, which I shall point out in the sequel of 



this chapter (see p. 265). 



Both iii the eastern and western hemispheres north of the 

 equator, when we carry our retrospect beyond the limits of 

 the tertiary rocks, and pass on to the antecedent cretaceous 

 formations, we find abundant proofs of an open sea in regions 

 which are now continental. . In the oldest part of this period 

 the south of England, we find in the Wealden strata 



memorials of the delta of a large river, 



mi 



m 



the 



contour of land and sea which has no reconcilable relation 



to existing geographical conditions; and it is worthy of 



note that, although the foundations of this delta sank during 



the accumulation of the fluviatile strata as much as 1,000 or 



sometimes 1,500 ft., yet there continued to be land in the 



neighbourhood in the south-east of England ; which can only 



be explained by supposing that an upward movement was 



taking place in the vicinity of a downward one, or that parts 



of the surface were moving slowly in two opposite directions. 



The frequent unconformability of successive strata of 

 different ages— those standing next in succession having so 

 often been deposited horizontally on the group which im- 

 mediately preceded, or, to speak more correctly, which in 

 our defective chain of known records stands, at present, next 

 in consecutive order— is a proof that if we had a series of 

 maps, in which a restoration of the physical geography of 

 thirty or more periods were depicted, they would bear 

 no more resemblance to each other or to the actual position 

 of land and sea, than does the map of one hemisphere at 

 present to that of the other. 



The height to which ammonites, shells, and corals have 

 been traced in the Alps, Andes, and Himalaya is sufficient 

 to show that the materials of all those chains were elaborated 



some oi them 



to 



Beds of coal, in the ancient carboniferous formation, were 

 derived, as we have seen in the last chapter, from plants 



swampy 



The 



them must 



