applied to the study of some Metamorphic Rocks. 1 75 



stances the original mineral substances from which it has been 

 derived. 



By this treatment, a siliceous skeleton is always left, in which 

 the mineral substances alluded to are nearly always enclosed; 

 on immersion in water, this skeleton becomes opalescent, and 

 exhibits many of the phsenomena of the skeletons already de- 

 scribed. 



This mode of treatment by various solvents enables us at 

 once to account for the variations which occur in many of the 

 published analyses of serpentine, as it must be evident that the 

 nature, quantity, and stage of decomposition of the enclosed 

 minerals must greatly vary. My experiments on this subject 

 are not as yet sufficiently advanced to offer more than a few 

 concluding remarks respecting some properties which I have 

 lately observed in connexion with the skeletons of several speci- 

 mens of serpentine. In two I have succeeded in detecting the 

 presence of organic matter under the action of concentrated 

 sulphuric acid. One of these is from the neighbourhood of 

 Holyhead, and the other from Snarum in Norway. The speci- 

 men from Norway is of a yellowish-green colour with undulating 

 lines of light green ; and its skeleton, which is almost entirely 

 soluble when submitted to the action of caustic potash, shows 

 small micaceous spangles of talc, and also black spots derived 

 from decomposed garnets. It absorbs about 40 per cent, of 

 water, becoming translucent, and is of a rather compact structure. 

 The serpentine from the neighbourhood of Holyhead, treated 

 with sulphuric acid, presents marks of carbonization ; but it is 

 only at certain isolated points, and the skeleton appears to pos- 

 sess the property of cleavage in certain definite directions. 



The serpentine of Galway, though of a variable character, is 

 more or less readily acted upon by acids, according to the state 

 of alteration which it has undergone, and the quantity of car- 

 bonate of lime which it contains, the latter being often uniformly 

 disseminated through the mass. The skeleton which it leaves 

 is in general very friable, and falls to powder on drying ; the part 

 not affected by the action of caustic potash is formed by an ag- 

 glomeration of micaceous spangles of talc, and also insoluble 

 silica. The green colour is produced chiefly by protoxide of 

 iron, which forms the irregular veins observable. 



In the serpentine of Penzance, coloured chieHy by peroxide 

 of iron, the siliceous skeleton envelopes a nucleus almost unaf- 

 fected by the action of acids, and which consists of an aggregation 

 of more or less altered diallagc and hornblende. 



By the simple process which I have endeavoured to describe, 

 namely the submission of thin lamiii;e to the iuHuencc of acids 

 and other solvents, true serpentines, which arc. hydrated mine- 



