THE GEOLOGIST. 
69 
beautifully crystallised, and possess both their grecu colour and their 
usual transparency. 
From these investigations, M. Daubree feels justified in concluding 
that a great number of silicates — perhaps all — found in the primitive 
crystalline rocks, have been formed by the influence of water at a high 
temperature; which temperature is, however, very inferior to that of 
the point of fusion of these silicates. He seems to think that the 
granite rocks themselves very probably owe their formation and 
crystalline appearance to similar causes. We must content ourselves 
here by indicating the result of experiment, and be silent as regards 
discussion. If the experiments just related, and which are being 
continued by JI. Daubree, are repeated with success, his conclusions 
will appear certainly very natural. The most striking feature in his 
paper is, without doubt, the formation, in the above circumstances, of 
feldspar — a rock so universally spread throughout nature, and which 
plays so important a part as constituent of almost all the primary or 
eruptive rocks. Although crystals of feldspar have been discovered in 
scorite, and, by Heine, in the refuse of a furnace for copper fusing,* 
it appears from Humboldt's statement f that they have never before 
been purposely formed : — "Nor have chemists," says he, "ever succeeded 
in artificially producing either feldspar or horneblend." It may be 
well to add that feldspar is daily formed under our eyes in the lava of 
volcanos. Since M. Daubree's observations have come to light, this 
must doubtless be attributed to the abundant quantity of water incor- 
porated in lava until it becomes completely solidified. 
M. Kuhlmann, of Lille, has published a long memoir on siliceous 
infiltration or petrifaction, and on epigenesis. J In this work the 
learned author, who has already done so much for the advancement of 
chemical and geological science, has presented us with nothing very 
new. He explains the curious phenomenon of petrifaction by the 
action of carbonic acid, or of carbonate of ammonia, on the silicates of 
potash and soda invariably found in spring water. A similar theory 
has been already professed and published by others, and, I believe, 
by M. Kuhlmann himself. 
The phenomenon of petrifaction is certainly one of the most curious 
processes in nature. Is it not wonderful to find the soft stem of 
* They were analysed by Kersten. f Cosmos, Vol. I. 
{ Comptes Rendus, Nov, 9, 1857. 
