GEOGRAPHICAL EVOLUTION 345 



this explanation be true, even for the enormously thick 

 and comparatively uniform systems of older geological 

 periods, the relatively thin and much more varied stratified 

 groups of later date can offer no difficulty. In short, the 

 more attentively the stratified rocks of the crust of the 

 earth are studied, the more striking becomes the absence 

 of any deposits among them which can legitimately be con- 

 sidered those of a deep sea. They have all been deposited 

 in comparatively shallow water. 



The same conclusion may be arrived at from a consider- 

 ation of the circumstances under which the deposition must 

 have taken place. It is evident that the sedimentary rocks 

 of all ages have been derived from degradation of land. 

 The gravel, sand, and mud, of which they consist, existed 

 previously as part of mountains, hills, or plains. These 

 materials carried down to the sea would arrange themselves 

 there as they do still, the coarser portions nearest the shore, 

 the finer silt and mud farthest from it. From the earliest 

 geological times the great area of deposit has been, as it 

 still is, the marginal belt of sea-floor skirting the land. It 

 is there that nature has always strewn " the dust of conti- 

 nents to be." The decay of old rocks has been unceasingly 

 in progress on the land, and the building up of new rocks 

 has been unintermittently going on underneath the adjoining 

 sea. The two phenomena are the complementary sides of 

 one process, which belongs to the terrestrial and shallow 

 oceanic parts of the earth's surface and not to the wide and 

 deep ocean basins. 



(2) Recent explorations of the bottom of the deep sea 

 all over the world have brought additional light to this 

 question. No part of the results obtained by the Challenger 

 Expedition has a pro founder interest for geologists and 

 geographers than the proof which they furnish that the 

 floor of the ocean basins has no real analogy among the 

 sedimentary formations that form most of the frame- 

 work of the land. We now know by actual dredging and 

 inspection that the ordinary sediment washed off the land 

 sinks to the sea-bottom before it reaches the deeper abysses, 

 and that, as a rule, only the finer particles are carried more 

 than % few score of miles from the shore. Instead of such 



