A. JR. Sunt — Vein- Quartz and Sands. 213 



In December, 1886, when examining marine sands, I pulverized 

 a flint pebble and several quartz-pebbles for the sake of comparison 

 in the microscope. I noted that the first quartz-pebble I examined 

 was full of enclosures with bubbles. Subsequently I hadjnore than 

 a dozen vein-quartzes sliced. Not only did they all contain bubbles, but 

 they all contained moving bubbles, the infallible proof of the presence 

 of fluid. Quartz-veins and granites are near of kin, and in 1889 1 wrote 

 a paper on granite. My interest in sands and granites led me to 

 appeal more than once to the most distinguished honorary member 

 of our local Society, Dr. H. C. Sorby, F.R.S., who was most unsparing 

 in his assistance in both of those subjects, which he had so long made 

 his own. However, as might be expected, the nut proved too hard 

 for me to crack. But Dr. Sorby's old correspondence has now put 

 me into no slight dilemma. I cannot publish it, and I can scarcely 

 absorb the ideas and dispense them as my own ; while the last thing 

 I should care to do would be to appear in the slightest degree to sit 

 in judgment on the master. Yet the only points which interest me 

 are those in which I do not quite understand Dr. Sorby ; the fault 

 being no doubt my own, if only for not having sought an explanation 

 direct. 



One point which has caused me much thought in the matter of 

 sands is the omission by Dr. Sorby of all mention of quartz-veins 

 as one derivation of quartz-sands, both in the addresses to the 

 Microscopical and Geological Societies. The same doubt arises in 

 the case of M. Delesse and the beaches of the French coast. We 

 hear much of hyaline quartz-sand, but nothing of vein-quartzes ; 

 yet vein-quartz seems an important constituent of grits and sandstones. 

 There are, moreover, many quartz-veins the sands derived from which 

 could not be distinguished from sands derived from granites, seeing 

 that water inclusions, carbonic acid inclusions, chlorides, and negative 

 crystals are found in both varieties. We need not flatter ourselves 

 that we can distinguish a granite quartz by its clearness and freedom 

 from opacity. Rock crystal is the clearest of quartz, and it is no 

 rare thing to find water-clear crystals and milkj' crystals lying side 

 by side in the same drusy cavity ; while between the two there may 

 be found elsewhere every gradation. When once we begin to reflect 

 on the whys and the wherefores of quartzes, we soon find ourselves 

 across the borders of the known, and I feel inclined to transfer to 

 quartz an observation by Dr. Sorby on granite, viz., that there 

 are many things connected with it about which we know much less 

 than is desirable. 



I believe that the most important paper on the subject is still 

 Dr. Sorby's short address of four pages to the Microscopical Society 

 in 1876, "On the Critical Point in the Consolidation of Granitic Rocks." 

 So far as I am aware, there are only two points in that paper that 

 have been reconsidered, and neither of them are of material importance, 

 so far as regards vein-quartz. Dr. Sorby followed Cagaiard de la 

 Tour in taking 412 C. as the critical temperature of watex-, whereas 

 Mr. Hartley, in the Report to the British Association in 1877, treats 

 it as being 342° C. Dr. Sorby also assumed that above the critical 



