216 Geological Society. 



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. 



I 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 1 will only observe, that they appear to me to 

 be attributed too exclusively to Plutonic action. The phenomena 

 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 

 Transformation of lias into saccharoid limestone seen in the Py- 

 renees. I think it unnecessary to detail to you the descriptions 

 which Mr. Murchison has given of the Changes of structure, or 

 even of substance, that take place at the Malvern Hills and at sundry 

 other places in Wales, and on the confines of Wales, frequently, 

 though not always, in the vicinity of trap and sienite, because they 

 are in general the same as have been observed repeatedly in other 

 districts. The phenomena at Old Radnor, the author remarks, are 

 very analogous to those of the Val di Fassa in the Tyrol. It may, 

 however, be proper to mention, not as a novelty, but as a circum- 

 stance the frequent occurrence of which is little attended to, that in 

 Carmarthenshire the line of altered rock produced by the proximity, 

 or as it is called the protrusion, of a mass of porphyritic trap, is pa- 

 rallel to the strike of the grauwacke so altered. At Caer Caradoc, 

 the Wrekin, the Stiperstones, and elsewhere, a stratified sandstone 

 is at its junction with trap converted into quartz rock. One other 

 circumstance deserves to be noticed; the range of the Stiperstones, 



