128 The Bed of the Ocean. 



period, and which apparently do not range beyond the loo- 

 lathom line. 



Formation of Sub-oceanic Strata. — Oscar Peschel, in his 

 remarkable essay on New Problems iit Comparative Geography, 

 has already expressed the opinion that the continents are older 

 than the mountain ranges we find upon them ; that the latter 

 have been raised up along the coast-lines of the former, 

 and that their elevation appears to be due to lateral pressure. 

 He al^o remarks that most of these coast-ranges are backed 

 on the land side by high plateaux. A study of the results of 

 recent deep-sea exploration will lead to the same conclusions. 



If there be little doubt that the currents of the ocean are 

 the carriers and distributors of temperature throughout the 

 vast depths of the seas which cover so large a portion of the 

 surface of our planet, it is equally clear that water in every 

 shape, from the smallest stream to the great oceanic rivers, is 

 the principal solvent, carrier, and distributor of the solid matter 

 which composes the only portion of the earth-crust with which 

 we are acquainted. The solid particles thus held in suspense 

 are deposited according to their weight and bulk — the heavier 

 ones first and nearest to the place whence they came, whilst 

 the lighter ones are carried to a greater distance. Those 

 which are light and yet bulky remain in suspense for some 

 time : if lighter than water, they will never reach the bottom ; 

 if a little heavier, they will do so only after a lapse of time, 

 longer or shorter according as the conditions are more or less 

 favourable. Chief amongst these conditions is the velocity 

 of the current of water which acts as the carrier of solid matter ; 

 the greater that velocity, the greater is the weight of the solid 

 particles held in suspense, and the greater is the distance 

 to which they are carried, and vice versa. 



The matter distributed by oceanic currents is mainly com- 

 posed of inorganic detritus, the result of sub-aerial and sub- 



