394 Geological Memoirs, 



composed of similar remains, and to resemble very closely the for- 

 mation of carboniferous limestone from Lake Onega. 



Amongst the stratified fossiliferous rocks therefore, it remained 

 only to exhibit similar relations with regard to the lower palaeozoic 

 rocks, where however the difficulty arising from the great amount of 

 chemical change such rocks have undergone, destroying the vestiges 

 of these minute creatures, besides the opaque and troublesome cha- 

 racter of the rock itself, renders the negative result at present ob- 

 tained little to be depended on. It is very possible that in the 

 lowest of the series of deposited rocks such minute bodies have suf- 

 fered change, but it is also highly probable that they have occasion- 

 ally been preserved, owing to some favourable circumstances, and 

 may therefore still be discovered. 



Beyond these limits it has been hitherto considered that all our 

 investigations must necessarily cease, the field of observation seem- 

 ing to be completely shut out in those cases where volcanic forces 

 have come into play. The calcareous rocks when exposed to heat 

 soon lose all indications of their having been formed by organized 

 beings, and the siliceous earth, when burnt in association with clay, 

 limestone and particles of iron, passes into a kind of glass, which, 

 whether compact or cellular, has the character of an entirely inor- 

 ganic mineral. It also appeared that the great depth at which it 

 was supposed volcanic products must be elaborated, rendered it im- 

 possible that any of the results of organization should be effected by 

 or should affect them. 



It is indeed several years since M. Ehrenberg stated to the Aca- 

 demy that the polishing slate and Kieselguhr ( siliceous sinter ), as well 

 as the so-called volcanic ashes or porcelain earth of volcanic districts, 

 might be considered as actually made up of the remains of these 

 little animalcules; but in the various places whence the specimens 

 had been obtained (near Cassel, the Caucasus, the Isle of France, 

 &c.) it seemed probable that they had been developed in great abun- 

 dance during the intervals between volcanic eruptions, the crater 

 under such circumstances becoming a small lake in which these ani- 

 mals lived and increased rapidly, and deposited their flinty skeletons, 

 another eruption after a time drying up the bed of such a temporary 

 lake, and covering it up with erupted ashes, which also in their turn 



