GEOGRAPHICAL DISTRIBUTION. 665 



Acadian fauna and a few in the Virginian fauna, as the 

 Labrador or polar current passes down along the coast, 

 bathing the New England coast north of Cape Cod, and 

 even extending under the warm surface-water as far as New 

 Jersey. On the other hand, the great volume of heated 

 tropical water forming the Gulf Stream issuing from the 

 Straits of Florida makes its influence most sensibly felt as 

 far as Cape Hatteras, and in a diminished degree to Cape 

 Cod, and even southern shells, etc., are found as outliers of 

 more southern faunas near Portland, Me., and Nova Scotia. 



As we descend from the shore into deep water, the tem- 

 perature becomes lower and lower the deeper we go, until 

 we come to a stratum or zone of water about o2-36 Fahr., 

 where circumpolar or arctic life alone abounds. Wherever 

 deep abysses off the coast or at the bottom of bays or gulfs 

 occur, the water is found to be colder than elsewhere ; just 

 as when we ascend a mountain the air becomes colder, un- 

 til at the Alpine summits we find an arctic temperature 

 and fauna ; thus, in the sea, increase of depth is paralleled 

 by increase of height on land. 



Usually, off the coast of the United States, north of New 



/ ' 



York, there is a distinct zone of life between high and low 

 water, a second extending to the depth of about fifty fathoms, 

 and a third to one hundred fathoms or over. At a depth of 

 from one or two hundred fathoms in the Northern Atlantic, 

 and from five hundred to one thousand fathoms in the sub- 

 tropical and tropical seas, down to the deepest parts of the 

 ocean, now known in a few points to be about five miles in 

 depth, the water is about 33 Fahr. and the animal life is 

 polar in its nature. The water of the ocean all over the 

 globe, as shown by the results of the " Challenger" and 

 other expeditions for the exploration of the sea at great 

 depths, everywhere below a depth of one thousand fathoms, 

 is of an arctic temperature, overlaid by the heated water of 

 the tropics. The abysses or deeper parts of the ocean-bed 

 support a nearly uniform assemblage of life, which may bt> 

 called the deep-sea or abyssal fauna. The animals largely 

 consist of Echinoderms, notably Crinoids, with Coelentcratrs, 

 mollusks, worms, and Crustacea, and it is an interesting fact 



