l^Q . 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 hmit the amomit of exposure 

 which they might bear, but they are unquestionably such 

 as to enable them to sustain hfe for several days, in the 

 case we have supposed. The eggs of snails have been 

 subjected to a high temperatui-e 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 part of it, apparently not exceeding an acre in 

 extent, Helix hortensis formerly existed in such numbers that hundreds 

 could be obtained in a few moments. On approaching the island at this 

 time, smoke was seen rising from it, and presently a rude hut erected on 

 the sheltered side, boats drawn up on the strand, nets spread upon the 

 bushes to dry, and lobster-traps scattered about, became \-isible, 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 

 hortensis is greatly reduced in numbers, and must very soon become ex- 

 tinct. After a diligent search of nearly an hour, only four or five living 

 specunens could be found. It may be well to mention in tliis place, that 

 the same effect has followed the connection of the small island near Niagara 

 Falls with Goat Island. Within two years after admission was thus gained 

 to it, the mollusks were nearly exterminated. 



