166 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



ocean, from the West Indies across the Atlantic to 

 our own coasts and on to Norway, by the dead 

 shells * which are strewn upon it all along their 

 course. 



In the tropics there are about forty species of 

 Foraminifera, Pteropods, and other carbonate-of- 

 lime-secreting organisms, which live in or near the 

 surface-waters of the ocean, whose dead shells make 

 up at times 80 to 90 per cent, of the deposit at the 

 bottom. 



As the Gulf Stream waters are cooled in passing* 

 northwards, many of these organisms die out or 

 become greatly dwarfed in form as they approach 

 the colder waters of the north ; still, in mid-ocean,, 

 between this country and Newfoundland, these shells 

 make up often 70 to 80 per cent, of the deposits. 



In the Faroe Channel, only seven or eight species 

 are found living on or near the surface ; but south 

 of the Wyville Thomson Ridge, and to the north of 

 this ridge in the central parts of the Norwegian 

 Sea, not much affected by the Arctic surface currents,, 

 they make up 30 to 40 per cent, of the deposit. The 

 influence of the Arctic currents moving from north 

 to south can be traced in like manner on the floor 

 of the Atlantic. By an examination of a deposit* 

 Dr. Murray has shown that it is possible to tell 

 approximately, from the character of the dead 

 shells of the surface organisms found in it, its 

 latitude and the depth from which it came ; while 

 its longitude can in many instances be approxi- 

 mately determined by careful microscopical exam- 

 ination of the fragments, organic and inorganic, of 

 which it may be composed. The warm Atlantic 

 water, passing over the Wyville Thomson Ridge to 

 the north-east, sweeps the crest of the ridge with 

 considerable force, regulated by the state of the 

 tides ; so great is this force that no mud or ooze is 

 deposited on the ridge, the small mineral particles 



* Chiefly the dead shells of Globigerinidse, PulvinulinidsB, 

 Pteropods, Heteropods, and other pelagic Mollusca. 



