APHORISMS AND REFLECTIONS 61 



raspberry, being formed of a number of nearly 

 globular chambers of different sizes congregated 

 together. It is called Giolrigerwa, and some speci- 

 mens of chalk consist of little else than Globigcn'iue 

 and granules. Let us fix our attention upon the 

 Globigerina. It is the spoor of the game we are 

 tracking. If we can learn what it is and what are 

 the conditions of its existence, we shall see our way 

 to the origin and past history of the chalk. 



It so happens that calcareous skeletons, exactly 

 similar to the Globigerina: 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 

 Globigerinue, 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 impera- 

 tively 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. 



Lieut. Brooke, of the American Navy, some years 

 ago invented a most ingenious machine, by which 



