NATURALIZATION OF AQUATIC ANIMALS—BEDS OF SHELLS. 117 
salt water spawn in fresh, and some fresli-water species, tlie 
common brook trout of New England for instance, which, 
under ordinary circumstances, never visit the sea, will, if trans¬ 
ferred to brooks emptying directly into the ocean, go down 
into the salt water after spawning time, and return again the 
next season. Sea fish, the smelt among others, are said to 
have been naturalized in fresh water, and some naturalists 
have argued from the character of the fish of Lake Baikal, and 
especially from the existence of the seal in that locality, that 
all its inhabitants were originally marine species, and have 
changed their habits with the gradual conversion of the 
saline waters of the lake—once, as is assumed, a maritime bay 
—into fresh.* The presence of the seal is hardly conclusive on 
this point, for it is sometimes seen in Lake Champlain at the 
distance of some hundreds of miles from even brackish water. 
One of these animals was killed on the ice in that lake in Feb¬ 
ruary, 1810, another in February, 1816,f and remains of the 
seal have been found at other times in the same waters. 
The remains of the higher orders of aquatic animals are 
generally so perishable that, even where most abundant, they 
do not appear to be now forming permanent deposits of any 
considerable magnitude ; but it is quite otherwise with shell 
fish, and, as we shall see hereafter, with many of the minute 
limeworkers of the sea. There are, on the southern coast of 
the United States, beds of shells so extensive that they were 
formerly supposed to have been naturally accumulated, and 
were appealed to as proofs of an elevation of the coast by geo¬ 
logical causes; but they are now ascertained to have been 
derived from oysters, consumed in the course of long ages by 
* Babinet, Etudes et Lectures , ii, pp. 108, 110. 
f Thompson, Natural History of Vermont , p. 38, and Appendix, p. 13. 
There is no reason to believe that the seal breeds in Lake Champlain, but 
the individual last taken there must have been some weeks, at least, in its 
waters. It was killed on the ice in the widest part of the lake, on the 23d 
of February, thirteen days after the surface was entirely frozen, except the 
usual small cracks, and a month or two after the ice closed at all points 
north of the place where the seal was found. 
