PRINCIPLES OF PALAEONTOLOGY. 



vegetable organisms (Polycystina and Diatoms). Though many 

 of the minute animals, the 

 hard parts of which form the 

 ooze, undoubtedly live at or 

 near the surface of the sea, 

 others, probably, really live 

 near the bottom; and the ooze 

 itself forms a congenial home 

 for numerous sponges, sea- 

 lilies, and other marine ani- 

 mals which flourish at great 

 depths in the sea. There is 

 thus established an intimate 

 and most interesting parallel- 

 ism between the chalk and 

 the ooze of modern oceans. 



Fig. 8. Organisms in the Atlantic Ooze, 

 chiefly Foraminlfera (Globigerinn and 



Both are formed essentially in Textularia), with 1 >olycystina and sponge- 

 the same way, and the latter ^ules; highly magnified. (Original.) 



only requires consolidation to become actually converted into 

 chalk. Both are fundamentally organic deposits, apparently 

 requiring a great depth of water for their accumulation, and 

 mainly composed of the remains of Foraminifera, together with 

 the entire or broken skeletons of other marine animals of greater 

 dimensions. It is to be remembered, however, that the ooze, 

 though strictly representative of the chalk, cannot be said in any 

 proper sense to be actuall}' identical with the formation so called 

 by geologists. A great lapse of time separates the two, and 

 though composed of the remains of representative classes or 

 groups of animals, it is only in the case of the lowly-organized 

 Globigerina, and of some other organisms of little higher grade, 

 that we find absolutely the same kinds or species of animals in 

 both. 



Limestone, like chalk, is composed of carbonate of lime, 

 sometimes almost pure, but more commonly with a greater or 

 less intermixture of some foreign material, such as alumina or 

 silica. The varieties of limestone are almost innumerable, but 

 the great majority can be clearly proved to agree with chalk in 

 being essentially of organic origin, and in being more or less 

 largely composed of the remains of living beings. In many 

 instances the organic remains which compose limestone are so 

 large as to be readily visible to the naked eye, and the rock is 

 at once seen to be nothing more than an agglomeration of the 

 skeletons, generally fragmentary, of certain marine animals, 



