CHAP. XV.] OF CONTINENTS AND OCEANS. 327 



did not anywhere rise to elevations of more than 6,000 feet 

 would be correctly called a continent. 



2. As to the second statement, it is perfectly true that the 

 marginal belts of comparatively shallow water which have 

 always surrounded the tracts of continental land have been 

 from the earliest geological times the principal areas of de- 

 position. It would indeed be very surprising if it were 

 otherwise, for most of the materials carried down from 

 any tract of land must come to rest within a certain dis- 

 tance of the shore, and thus geological deposits are chiefly 

 shore deposits. Dr. A. G-eikie, however, goes farther, and 

 remarks that " the more attentively the stratified rocks of 

 the earth are studied, the more striking becomes the absence 

 of any formations among them which can legitimately be 

 considered those of a deep sea. They have all been de- 

 posited in comparatively shallow water." ] This also is 

 probably true if by comparatively shallow water Dr. 

 G-eikie means any depth not exceeding 1,000 fathoms. 

 Compared with the depth of modern ocean-troughs water 

 of only 700 or 800 fathoms is shallow, but it might fairly 

 be called a deep sea ; and, as. we shall presently see, there 

 is at any rate one formation which was probably formed in 

 a sea of at least that depth. 



The absence or rarity of deep-sea deposits is in fact more 

 conspicuous among Palaeozoic than Neozoic rocks, but this 

 fact can hardly be taken as evidence of the fixity of oceans 

 and continents ; it would be more logical to regard the 

 absence of such deposits as evidence of the absence of 

 oceans, and to suppose that in these early times the relative 

 proportion of land was greater than it is now, or that the 

 arrangement of land and sea was such that neither covered 

 very large spaces of the earth's surface. 



3. That Dr. Wallace should seriously argue that " de- 



1 " Geographical Evolution, Proc. Roy. Geograph. Soc.," 1879, p. 426. 

 The italics are mine. 



