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time. The justice, or at least the relevancy of the reasoning, depends 

 on the establishment of many postulates which in the present state 

 of our knowledge can be regarded only as matters of surmise: but 

 I treated this subject so much at large on a former occasion, that I 

 will not detain you with any further observations upon it now. 



A Paper by Dr. Turner, our Secretary, informs us of some expe- 

 riments which have been made on the action of high-pressure steam 

 upon glass, and other siliceous compounds. The glass was suspended 

 within the boiler of a steam-engine, encased in wire gauze at a tem- 

 perature of about 300" commonly for ten hours a day. At the end 

 of four months all the pieces were decomposed, and the plate-glass 

 especially, consisting of silex and soda, was in some pieces corroded 

 entirely through. Window-glass was less acted upon, and rock 

 crystal wholly unaltered. Dr, Turner ascribes these changes to the 

 influence of the water on the alkali of the glass, the white opaque 

 matter with which the decomposed pieces were coated being siliceous 

 earth entirely free from alkali; but some portions of the silex also 

 must have been dissolved, for the apertures of the gauze were in 

 some instances closed by a siliceous incrustation, and a small sta- 

 lactite of silica was found depending from the lowest part. He points 

 out the bearing of these results on the agency of water under high 

 pressure on felspathic and other rocks containing alkalies, and in this 

 point of view they are of great interest. 



J hail with unfeigned pleasure the arrival of every paper which 

 makes geology a science not merely of observation, but experiment. 

 In the condition in which we stand at present, the geology of the 

 laboratory is as essential to our progress, as that of the open air. 



The Metamorphoses of rocks which are so continually pressed 

 upon our notice are capable of explanation by chemists only. Of 

 those metamorphoses I will only observe, that they appear to me to 

 be attributed too exclusively to Plutonic action. The phaenomena 

 which startle and delight us in the vicinity of whin dykes, we regard 

 in Neptunian rocks without emotion. 



The Account recently published by Professor Hoffmann of the 

 marble of Carrara is very striking. The result of his examination 

 is, that this pure saccharine limestone in which no trace has been 

 discovered of organic matter, although in its cavities are occa- 

 sionally found pellucid crystals of quartz, is only transformed oolite. 

 Mr. De la Beche's researches along the gulf of Spezia, an account 

 of which is published in the Transactions of the Geological Society 

 of France, had already prepared us for such an announcement : yet 

 it seems strange when we reflect on the wide expanse of serpentine 

 which is seen in its neighbourhood, that the Carrara marble should 

 not be magnesian. In the Isle of Skye veins of serpentine sometimes 

 penetrate the lias, where, in the vicinity of numerous whin dykes it 

 assumes the whiteness and occasionally the sparkling grain of statuary 

 marble, and here again the marble is unadulterated by magnesia : 

 the origin of the serpentine is somewhat less mysterious since the 

 limestone in its unaltered state is micaceous. M. Dufrenoy in a 

 late number of the " Annales des Mines," has described a similar 



