55 2 THE POPULAR SCIENCE MONTHLY. 



torn of a sun-dried, muddy pool. These phenomena unequivocally 

 point to shallow and even littoral waters. They occur from bottom 

 to top of formations which reach a thickness of several thousand feet. 

 They can be interpreted only in one way, viz., that the formations in 

 question began to be laid down in shallow water ; that during their 

 formation the area of deposit gradually subsided for thousands of feet ; 

 yet that the rate of accumulation of sediment kept pace on the whole 

 with this depression ; and hence, that the original shallow-water char- 

 acter of the deposits remained, even after the original sea-bottom had 

 been buried under a vast mass of sedimentary matter. Now, if this 

 explanation be true, even for the enormously thick and comparatively 

 uniform formations of older geological periods, the relatively thin and 

 much more varied formations 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 formations 

 among them which can legitimately be considered those of a deep sea. 

 They have all been deposited in comparatively shallow water. 



The same conclusion may be arrived at from a consideration 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 the 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 strewed " the 

 dust of continents to be." The decay of old rocks has been unceas- 

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

 been as unintermittently going on underneath the adjoining sea. The 

 two phenomena are the complementary sides of one process, which be- 

 longs to the terrestrial and shallow oceanic parts of the earth's surface 

 and not to the wide and deep ocean-basins. 



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 profounder 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 which form most of the framework 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 

 a few score of miles from the shore. Instead of such sandy and pebbly 

 material as we find so largely among the sedimentary rocks of the land, 

 wide tracts of the sea-bottom at great depths are covered with various 

 kinds of organic ooze, composed sometimes of minute calcareous f orami- 



