156 INTRODUCTION. 
That this hypothesis of the agency of currents is no 
violent one, is proved by common experience. A single 
log of timber, removed from the bank of a river by the 
rise of its waters during a freshet, and borne by them 
to the ocean, and driven by winds, tides, and currents, 
might carry -with it, and deposit upon other shores, the 
eggs of mollusks, or even the living animals themselves, 
provided they were not too long exposed to the elements. 
It is difficult to estimate their powers of endurance under 
such circumstances, or to limit the amount of exposure 
which they might bear, but they are unquestionably such 
as to enable them to sustain life for several days, in the 
case we have supposed. The eggs of snails have been 
subjected to a high temperature in an oven, until, being 
totally deprived of moisture, they were friable between 
the fingers ; they have been repeatedly frozen and 
thawed again; they have been suffered to remain a con- 
constant shade. On this purl of it, apparently not exceeding an 
extent, Helix hortensis formerly existed in such numbers that hundreds 
could be obtained in a lew moments. On approaching the island at this 
time, smoke was seen rising from it, and presently a rude hut ere 
the sheltered side, boats drawn up on the strand, nets spread upon the 
bushes to dry, and lobster-traps scattered about, became visible, and an- 
nounced that a fisherman had taken possession of it. The usual conse- 
quence of the presence of man and his companions has followed. Helix 
Iwrtensis is greatly reduced in numbers, and must very soon become ex- 
tuiet. Alter a diligent search of nearly an hour, only four or five living 
specimens could be found. It may be well to mention in this place, that 
the same eflect has followed the connection of the small island near Niagara 
Falls with Goat Island. Within two years after admission was thus gained 
10 it, the mollusks were nearly exterminated. 
