84 THE HISTORY OF THE NORTH ATLANTIC 



of 1,200 to 2,000 fathoms. The stones, some of them glaci- 

 ated, were granite, diorite, amphibolite, mica schist, gneiss and 

 quartzite. This deposit ceases and gives place to Globigerina 

 ooze and red clay at 46° to 47° S., but even farther north there 

 is sometimes as much as 49 per cent, of crystalline sand. In 

 the Labrador current a block of syenite, weighing 400 lbs., was 

 taken up from 1,340 fathoms, and in the Arctic current, 100 

 miles from land, was a stony deposit, some stones being 

 glaciated. Among these were smoky quartz, quartzite, lime- 

 stone, dolomite, mica schist, and serpentine ; also particles of 

 monoclinic and triclinic felspar, hornblende, augite, magnetite, 

 mica and glauconite, the latter, no doubt, formed in the sea 

 bottom, the others drifted from Eozoic and Palaeozoic forma- 

 tions to the north.^ 



A remarkable fact in this connection is that the great depths 

 of the sea are as impassable to the majority of marine animals 

 as the land itself. According to Murray, while twelve of the 

 Challenger's dredgings, taken in depths greater than 2,000 

 fathoms, gave 92 species, mostly new to science, a similar 

 number of dredgings in shallower water near the land, give no 

 less than 1,000 species. Hence arises another apparent para- 

 dox relating to the distribution of organic beings. While at 

 first sight it might seem that the chances of wide distribution 

 are exceptionally great for marine species, this is not so. Ex- 

 cept in the case of those which enjoy a period of free locomo- 

 tion when young, or are floating and pelagic, the deep ocean 

 sets bounds to their migrations. On the other hand, the 

 spores of cryptogamic plants may be carried for vast distances 

 by the wind, and the growth of volcanic islands may effect 

 connections which, though only temporary, may afford oppor- 

 tunity for land animals and plants to pass over. 



With reference to the transmission of living beings across 

 the Atlantic, we have before us the remarkable fact that from 

 * General Report, '* Challenger " Expedition. 



