XVI.] FORAMINIFERAL LAND. 267 



absent towards the northern or the southern limits of this 

 range. 



Over the whole of this enormous extent of the ocean, 

 therefore, we must imagine an incessant rain of Globigerina 

 shells j which, after falling from the surface, through perhaps 

 two or three mi^s of sea-water, at length rest in, and add to, 

 the ooze at the bottom. It is probably an over-estimate if 

 we assume that the average bulk of the calcareous matter 

 contained in each full grown Globigerina amounts to 

 T.ow.inroth of a cubic inch. Nevertheless, the example of 

 the effect of pluvial denudation, however slow and insig- 

 nificant the wear and tear of rain and rivers on dry land 

 may appear to be, when continued through long ages, in 

 destroying the solids of the globe, prepares the mind to 

 view, in this incessant downpour of lime-drizzle, a no less 

 potent agent of reconstruction. If we suppose that the 

 total thickness of the deposit of solid matter on the sea- 

 bottom, arising from the foraminiferal shower, is as much as 

 one-tenth of an inch a year; then, if the present state of the 

 Atlantic and Pacific oceans has existed for only 100,000 

 years, tliis apparently unimportant operation will have 

 sufficed to cover their floors with a bed of limestone no 

 less than eight hundred feet thick. 



Although the Globigerina shells constitute the greater 

 part of the substance of the ooze, the remains of other or- 

 ganisms are found with themi. Among these, other Foramini- 

 fera are very common ; and especially one form, the Orbiilina, 

 Fig. 79 B, which is very closely allied to, if not a condition 

 of, the Globigerina itself. 



Besides these, there are innumerable multitudes of very 

 minute saucer-shaped disks, termed coccoliths, which are 

 frequently met with associated together into spheroidal 

 aggregations, the coccospheres of Wallich, Fig. 79 C, D. 



