X INTRODUCTION. 



up only stones and earth from the land, like the moraine 

 of a glacier, such a conjecture does not seem to be en- 

 titled to much weight. An iceberg might certainly be 

 stranded, and thus pick up shells ; but it would in all 

 probability be dissolved on the spot in the course of time. 

 Its bulk and weight are too great to admit of its floating 

 off again under such circumstances as I have supposed. 

 It is, indeed, within the bounds of possibility that the 

 shells might have been collected on the shore by coast- 

 ice, and carried off to sea ; but Dr. Wallich informs me 

 that this kind of ice has never been known to travel so far 

 southward as the locality above mentioned. There is 

 much greater probability that the mollusca in question 

 lived and died on the sea-bottom where their remains 

 were found. Every one who considers the importance of 

 these researches ought to read and study Wallich's trea- 

 tise on the North- Atlantic Sea-bed, and especially the 

 chapter on the bathymetrical limits of animal life in the 

 ocean. He will find the subject treated in a philosophical 

 and masterly style ; and the account of living starfishes 

 having been discovered at a depth of 1260 fathoms in 

 the open sea, and also the geological application of that 

 discovery, especially deserve attention. Until of late 

 years the use of the dredge, as an instrument of zoolo- 

 gical research, was nearly unknown. All that natu- 

 ralists did in former times was to examine the refuse of 

 trawl nets, which seldom reached a depth of 20 fa- 

 thoms ; or now and then fishing-lines of more than twice 

 that length brought to the surface a few shells and 

 corals which were accidentally detached from the bottom 

 of the sea. These specimens (as Professor Forbes said) 

 " only served to whet our curiosity, without affording 

 the information we thirsted for." Now-a-days, how- 

 ever, the dredge is a scientific necessity ; and scarcely 



