74 GEOLOGICAL MEMOIRS. 



mersen as mountain limestone, and in which Choristites mosquensis 

 is present in great beauty, has certainly been formed for the most 

 part by these microscopic animalcules ; and it is not long since Prof. 

 Bailey of New York forwarded to Europe specimens of a hornstone 

 from near Madison, Wisconsin, U.S., considered by the American 

 geologists as belonging either to the carboniferous or oolitic group ; 

 and this M. Ehrenberg on examination has found to be also entirely 

 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 opake 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 occa- 

 sionally 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 aftected 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 abundance 

 during the intervals between volcanic eruptions, the crater under 

 such circumstances becoming a small lake in which these animals 

 lived and increased rapidly, and deposited their flinty skeletons, 

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

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

 afterwards became the receptacle of a similar deposit. This it was 

 thought might go on until a more powerful and energetic upheaval 

 of the bottom of the crater either gave to these strata a steep inclina- 

 tion or fairly lifted the concave bed into a convex dome, thus pre- 

 cluding any further repetition of the process. It appeared, indeed, 

 from an examination of its internal structure, that the hornstone- 



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