162 



ORGANIC AGENCIES. 



these seem to be living, or recently dead ; some dead and empty, but 

 still perfect ; but most of them completely disintegrated. On account 

 of the great abundance of the shells of one form of f oraminif era, this 



Fig. 129.— Shells of living Foraminifera : a, Orbvlina universa, in its perfect condition, showing 

 the tubular spines which radiate from the surface of the shell; b, Globigerina bulloides, in its 

 ordinary condition, the thin hollow spines which are attached to the shell when perfect having 

 been broken off; c, Textularia variabilis ; d, Peneroplis planatus ; e, Rotalia concamerata ; f, 

 Cristellaria subarcuatula. Fig. a is after Wyville Thomson; the others are after Williamson. 

 All the figures are greatly enlarged (after Nicholson). 



soft, white mud is called globigerina ooze. Mingled in considerable 

 numbers among the calcareous shells are others of silica. These are 

 also partly animals (radiolaria) and partly plants (diatoms). The ex- 

 traordinary resemblance of this deep-sea ooze, both in chemical and 

 microscopic character, to chalk, leaves no room for doubt that chalk 

 was formed in this way. 



