ORGANIC AGENCIES. 117 



very abundant, and deposits of these shells are formed 

 comparatively rapidly. 



Application. In many countries, and nowhere more 

 abundantly than in California, is found a soft, white, very 

 light and friable earth, often many feet in thickness and 

 many square miles in extent, which, under the microscope, 

 is seen to consist wholly of shells some perfect, some 

 broken of diatoms. It is only by the study of deposits 

 now forming that we may hope to understand the condi- 

 tions under which these remarkable deposits were formed. 



Deep-Sea Deposits. Many deep-sea explorations 

 have been recently undertaken by the governments of 

 Europe and the United States. From these we learn 

 that the deep-sea ooze is almost everywhere a fine white 

 mud, which dried looks like chalk, and under the micro- 

 scope is seen to be mainly composed of the carbonate-of- 

 lime shells some perfect, 

 more broken, most of all 

 comminuted of Forami- 

 nifera (a low form of ani- 

 mals). The most abun- 

 dant form is Globigerina 

 (Fig. 64), and therefore 

 this ooze is often called glo- 

 Ugerinaooze. Among these 



are Scattered silicious shells (Agassiz after Murray and Renard.) 



of diatoms and several other 



kinds of shells, animal and vegetable. All of these prob- 

 ably live at the surface, and on their death drop to the bot- 

 tom. So that we may imagine a continual drizzle of these 

 shells falling to the bottom. These deposits are certainly 

 of enormous extent, and probably of great thickness. 



Application. There is one geological stratum which 

 bears a striking resemblance to this deep-sea ooze, viz., 

 the chalk of England, France, the interior of Europe, and 

 our own western plains. The origin of this very peculiar 



