268 PHYSIOGRAPHY. [chap. 



The exact nature of these very curious bodies is not at 

 present known. 



In addition to the calcareous organic remains which 

 constitute the greater part of the ooze, it contains multi- 

 tudes of siliceous skeletons, some of which belong to simple 

 animal forms, such as Radiolaria and sponges, while others 

 are vegetable organisms, belonging to the group of Diatoms 

 described in the last chapter. The Diatoms and the Radi- 

 olaria inhabit the surface of the ocean, along with the 

 Globigeritice and OrbiilincB, but the sponges live at the 

 bottom. Here and there, the remains of other animals 

 which inhabit the depths, of the sea, such as starfishes, 

 sea-urchins, and various shell-fish, are also imbedded in 

 the ooze, and contribute to the solid submarine deposit. 



It is very interesting to remark that, just as the process of 

 pluvial denudation is only, in part, a conversion of solid into 

 fluid matter, and, for the rest, effects a mere transference of 

 solids ; so, the process of reconstruction of solids, which 

 takes place in the superficial parts of the ocean, by the 

 agency of the Globigerina, is not permanent. In other 

 words, there is reason to believe that the Globigerina shells 

 in the ooze, at the bottom of the sea, do not represent all 

 the work in the way of withdrawing calcareous matter 

 from solution in sea-water, which has been done by the 

 Globigerina at its surface. 



It has been seen that living GlobigeriiicB are found in 

 the uppermost stratum of the sea, all over the warm and 

 temperate parts of the world. Hence, it would seem to 

 follow, that Globigerina-ooze should' be found covering the 

 bottom of the sea over the whole of these regions ; and, in 

 fact, it is met with, at all depths, between 250 and 2,900 

 fathoms, over an immense extent of both the Atlantic and 

 the Pacific oceans. 



