278 UTILIZATION OP MINUTE LIFE. 



agate, or of certain flints, exhibits, in a beautiful 

 manner, the structure of a sponge. Dr. Bower- 

 bank's views on this subject are very clearly ex- 

 pressed in his paper read before the British Asso- 

 ciation in 1856, in which he brings forward 

 numerous proofs of his theory, and to which I must 

 refer my readers for the details. I agree with this 

 author that sponges doubtless have, at various 

 periods of the earth's history, largely contributed 

 towards the formation of agates and flints ; but it is 

 evident, at the same time, that other siliceous de- 

 posits, such as those of fossil infusoria, etc., have a 

 very different origin. 



Flints generally contain numerous fossil infu- 

 soria, and indeed their formation has often been 

 attributed to the remains of these animalculse. At 

 the same time, sponges appear to have contributed 

 also to the formation of these curious stones ; and 

 here is a curious fact in relation to this : In the 

 south of Europe, the beds of marl which alternate 

 with the white chalk consist of myriads of siliceous 

 shells of Infusoria and Diatomacece, and flints are 

 wanting ; whilst in the north of Europe the reverse 

 is found to be the case beds of flint are met with, 

 and marls with infusoria are wanting. 



Flints not only show beautifully-preserved re- 

 mains of sponges, but also those of polypes, such 

 as Alcyonia 3 etc., Echinia, and other marine organ- 



