AMERICAN AND WEST INDIAN FAUNA AND FLORA. 119 



On the Atlantic shores of the United States we have on a 

 more extended scale a repetition of the phenomenon first ob- 

 served in the Faeroe Channel by the "' Lightning," of the dif- 

 ference produced on the character of the fauna by a change of 

 temperature. The " warm and the cold areas," as they have 

 been termed there, find their parallel on our coast as seen in 

 the extension of the West Indian fauna along; the line of the 

 continental slope bathed by the Guli Stream, flanked on either 

 side by the arctic fauna living in the colder water of the bottom 

 of the Gulf Stream on the east, and in the cold arctic waters 

 which bathe the continental plateau within the sixty-fathom line 

 on the western edge of the area occupied by this more tropical 

 fauna. This shows in a remarkable way the powerful influence 

 exerted by the action of the heated water of the Gulf Stream 

 in extending to the northward, along the bottom, the range of 

 the fauna of a more southern latitude. This action is not 

 limited to the bottom, for on the surface also the character- 

 istic pelagic fauna is carried northward. The larvae of many 

 of the Caribbean and Mexican animals which swim, find an 

 abode as far north as the conditions of the water and the 

 bottom will allow ; the adults may also, little by little, creep up 

 northwards. 



This northern extension of the southern fauna has been care- 

 fully studied by the United States Fish Commission along the 

 southern coast of New England ; their dredgings have proved 

 the existence in this region of many animals known before only 

 from Florida, and of others which were previously considered 

 as characteristic tropical types. In fact, we have a northern ex- 

 tension, off the southern coast of New England, of the West 

 Indian and Gidf Stream fauna. The warm belt extending 

 from sixty-five to one hundred and twenty fathoms has an 

 equable temperature during the whole year, due to the action of 

 the Gulf Stream, while on the inshore plateau arctic animals 

 are found identical with those occurring at similar depths 

 north of Cape Cod, which flourish only in a variable but cold 

 temperature. Below the warm belt the temperature is uni- 

 formly cold, and passes into that of the general abyssal region 

 beyond it. The warm belt is but the northern extension of 



