J. 



ISO LAY SERMONS, ADDRESSES, AND REVIEWS. [ix. 



■ 



If any one were to try to persuade you that an oyster- 

 shell (which is also chiefly composed of carbonate of 

 lime) had crystallized out of sea-water, I suppose you 

 would laugh at the absurdity. Your laughter would 

 be justified by the fact that all experience tends to 

 show that oyster-shells are formed by the agency of 

 oysters, and in no other way. And if there were no 

 better reasons, we should be justified, on like grounds, 

 in believing that Globigerince is not the product of any- 

 thing but vital activity. 



Happily, however, better evidence in proof of the 

 organic nature of the Globigerince than that of analogy 

 is forthcoming. It so happens that calcareous skeletons, 

 exactly similar to the Globigerince of the chalk, are 

 being formed, at the present moment, by minute living 

 creatures, which flourish in multitudes, literally more 

 numerous than the sands of the sea-shore, over a large 

 extent of that part of the earth's surface which is 

 covered by the ocean. 



The history of the discovery of these living Globi- 

 gerince, and .of the part which they play in rock 

 building, is singular enough. It is a discovery which, 

 like others of no less scientific importance, has arisen, 

 incidentally, out of work devoted to very different and 

 exceedingly practical interests. 



When men first took to the sea, they speedily learned 

 to look out for shoals and rocks; and the more the 

 burthen of their ships increased, the more imperatively 

 necessary it became for sailors to ascertain with precision 

 the depth of the waters they traversed. Out of this 

 necessity grew the use of the lead and sounding line ; 

 and, ultimately, marine-surveying, which is the recording 

 of the form of coasts and of the depth of the sea, as 

 ascertained by the sounding-lead, upon charts. 



At the same time, it became desirable to ascertain 



