ANNUAL ADDRESS, MDCCCLXXI, 23 



tinguished. One furnished with a silicious coating is found 

 chiefly in fresh water, the other provided with, in by far 

 the great majority of species, a calcareous investment, is 

 almost limited to sea water. The former are known as 

 the diatomea3 or diatomacege; the latter as the foramini- 

 fera or polythalamia. There is beside a third group, 

 characterised by having a mineralised framework giving 

 support to the tender living animal matter described under 

 the name of polycystina. 



The mud of rivers and ponds is usually rich in diatoms, 

 and the mud dredged from the bottom of the sea is even 

 more prolific in foraminifera. As after the death of the 

 beings their cases remain, it follows that there must be a 

 progressive accumulation of emptied shells. What such 

 accumulations may amount to, and what an amount of 

 prolific microscopic life may be imperceptibly proceeding, 

 is displayed by deposits from still living aggregations of 

 such organisms, and still more forcibly by their debris as 

 found fossilised in various geological formations, dating back 

 to the remotest period, though more common in deposited 

 rocks of the tertiary series. 



The length to which this address has extended warns 

 me of the necessity of curtailing greatly the illustrations 

 that could be furnished of the facts just stated. I will 

 first quote an example from Dr. Hooker of existing opera- 

 tions of diatoms in building up strata remarkable for their 

 extent. "The waters" (Dr. Hooker writes), "and espe- 

 cially the newly-formed ice of the whole Antarctic Ocean, 

 between the parallels of 60 and 80 degrees south, abound 

 in diatomaceaa so numerous as to stain the sea every- 

 where of a pale ochreous brown, the surface having that 

 colour as far as the eye can reach from the ship * * * 



