1893.J NEW-YORK MICROSCOPICAL SOCIETY. 109 



dition in the fossil deposits of any other known region of the 

 globe ? Notice also the power of the Foraminifera to secrete cal- 

 careous shells, and of the Spongidge to secrete calcareous spicules, 

 and we can infer that the animal protoplasm of the Protozoa has 

 the power to elaborate out of their surrounding fluids the neces- 

 sary shields or frames best adapted to their vicissitudes. 



Against all of these positive and convincing data we can con- 

 trast nothing of an analogous kind in plant life. It would be 

 useless to refer to the power of certain plants that flourish in 

 ditches and marshes, and in tropical and semi-tropical regions, as 

 the Eqiiisetacece, or the canes, bamboos, and cereals, whose cuti- 

 cular surface is a layer of vegetable silica. I believe that there is 

 not any analogy between the power of the protoplasm of the 

 Diatomacese to assimilate oxide of silicon as an integral part of 

 its life, and the power of the plants named above to secrete what- 

 ever silica there may be in their woody structure; while there is 

 abundant evidence of the animal protoplasm having in an eminent 

 degree, and almost exclusively so, the power to appropriate from 

 fresh or salt water the requisite silica needed in its life cycle. 



But what has already been adduced does not reach the inferen- 

 tial bounds of the subject. Convictions often arise from fortui- 

 tous sources to round up a final conclusion. And as the diatomist 

 accumulates fresh experiences year by year, he may group his facts 

 in aiding him to some final conclusion or to reinforce some spe- 

 cial view. 



It is at this stage of the inquiry that the question comes up, 

 Why is it that in nearly every known marine fossil diatomaceous 

 deposit the silicious skeletons of the Diatomaceae form the major 

 part of the deposit, with few exceptions ? The main exception 

 is where the proportion of the diatoms in the deposit is less than 

 the other fossil organic remains derived from the recognized rhi- 

 zopods. What construction and interpretation are we justified 

 in putting upon the fact that when we analyze any given fossil 

 marine deposit we invariably find the following derivatives of the 

 Rhizopods, viz., silicious Polycystinse, or more properly Radio- 

 laria, silicious sponge spicules, and silicious Diatomaceae, to- 

 gether with calcareous foraminifera, invariably, or at least with 

 few exceptions, associated in deposits of extraordinary thickness ? 

 Of two of these typical deposits I can justly claim that, at the 



