578 PHYSICAL GEOGRAPHY. 



them. A variety of splendid colours in bright weather indicates their presence at the 

 surface of the sea, and a pale phosphoric light denotes the same in calm dark nights. 

 This is caused by the oily substance thrown off by the fish, which is spread over their 

 columns, and seems as if a dimly white napkin lay upon the deep. Some idea may be 

 formed of the number of individuals in the herring shoals, from the fact mentioned by 

 Lacepede, that the Norway fishermen capture four hundred millions in most years, and that 

 at Gottenburgh and its vicinity seven hundred millions are annually taken ; but both these 

 sums together are insignificant when compared with the gross amount captured by the 

 other European nations. The migrations of several kinds of fish lead them out of their 

 native element to wander over the land in quest of food, or of a more convenient habita- 

 tion. N Thus the common eel at night will forsake the water to traverse the meadows, 

 feeding on the snails it finds in its passage ; and when the pools become dry in seasons of 

 drought, some of the Siluridan family quit their old residence, in search of another, from 

 which the water has not been evaporated. Upon the coast of Coromandel, a kind of perch, 

 Perca scandens> leaves its liquid- home for the shore, and even climbs up the palm-trees 

 in pursuit of the small crustaceans upon which it feeds an enterprise to which its 

 organisation is expressly adapted. In the West Indies and South America, the land 

 crabs quit the mountains regularly once a year, march down to the sea-side in a body of 

 some millions at a time, directing their march with the right-lined precision of the 

 geometer, travelling chiefly in the night, the object to be attained being the deposition of 

 their spawn in the ocean. 



It may be allowed here to notice those animals which are classed with the warm-blooded 

 mammalia, yet whose residence is usually or exclusively marine, and whose forms are as 

 characteristic of the fish as of the quadruped. Of these, the whale tribes, the narwal or sea- 

 unicorn, the sea-horse, the phoca or sea-calf, and the dolphin, are the principal examples. 

 The former gigantic animals occupy the high latitudes of the ocean, and are character- 

 istically different in the north polar seas from their brethren in antarctic regions. 

 Incessantly pursued by man, as affording materials that are of high value in the arts of 

 life, the common whales have deserted their old^ haunts, and retired farther north, under 

 the pressure of danger, to the protection afforded by the perpetual ice. Notwithstanding 

 their vast size, these leviathans of the deep dive with prodigious rapidity to the bottom of 

 the soundless sea, and often in frolicsome gambols elevate the whole of their enormous 

 mass entirely out of the water with the exception of the tail-fins, falling down sideways 

 with a noise resembling that of a distant broadside. The seals, and other animals of the 

 Phocce tribe, are widely diffused, but those which inhabit the waters of the north differ 

 from the members of the same family which have their station in the southern seas, and vary 

 in their habits from those found within the tropics, the tropical species being solitary 

 individuals, while the polar associate in herds consisting of many thousands. It has been 

 thought a difficulty by naturalists, that inland seas, like the Caspian and the Lake Aral, 

 should have marine mammalia, the Phocce vitulince or sea-calves, identical with those 

 found in the Euxine and the Mediterranean ; and to account for their appearance in those 

 localities, the assistance of subterranean channels of communication between them has 

 been conjectured. But Mr. Lyell justly remarks, that as the occurrence of wolves and 

 other noxious animals on both sides of the British channel was adduced by Desmarest as 

 one of many arguments to prove that England and France were once united, so the 

 correspondence of the aquatic species of the inland seas of Asia with those of the Black 

 Sea tends to confirm the hypothesis, for which there are abundance of independent 

 geological data, that those seas were connected together by straits at no remote period of 

 the earth's history. To the same order of animals, the Manatus americanus and Halicore 

 Dugong, or sea-cow, belong ; the former abounding in the Orinoco, and the latter in 



