212 A. R. Hunt — Vein-Quartz and Sands. 



position (ibid., fig. 4), affords some support for the view that the? 

 extension of the magma proceeded by quiet diffusion rather than by 

 forcible injection. 



An explanation would also be found for the occurrence of lenticle& 

 of granite in complete isolation from the parent mass. 



The experiments quoted lead us to expect that diffusion might 

 go on even after solidification, seeing that in such a complex a high 

 temperature would be maintained for a long time, thus extending 

 the permeation zone yet further, and in perhaps an even subtler 

 manner. Indeed, what we know of the changes that have certainly 

 gone on in solid rocks shows that the solid state is no obstacle to 

 extensive molecular change.^ 



The principal difficulty would be this. The solids of the ex- 

 periments were homogeneous, being pure metals, so that diffusion took 

 place between molecules of only one kind on either side. Whether 

 the liquid magma of a granite was a completely homogeneous 

 liquid we do not know, but certainly after solidification no granite 

 is a homogeneous solid. Molecules of at least three kinds would 

 therefore, it would appear, have to diffuse in order to convey 

 granitoid matter from place to place, and that in due proportion. 

 This is certainly a difficulty, though not an impossibility. 



Moreover, are we quite sure that solid diffusion would be obliged 

 to proceed in this way ? At the close of the paper by Mr. Home 

 and myself to which reference has been made, it was pointed out 

 (ibid., pp. 647-8) how little is known of the chemistry of the 

 compounds of silicon, and how very much may be hoped for from 

 an extension of that knowledge, when we consider the chemical 

 analogies presented by that element and the part which it plays 

 in Nature.- 



V. — Vein-Quaktz and Sands. 

 By A. E. Hunt, M.A., F.G.S. 



SOME time ago my friend Mr. Jukes-Browne asked me to examine 

 some sand, with a view to ascertaining whether it was derived 

 from Dartmoor, Dartmoor quartzes have so many specific characters 

 that it is often easy to say that a quartz is not derived from that 

 region ; but owing to the fact that quartz-veins have not been studied, 

 it is usually impossible to say whence various sands have in fact come. 

 In the course of conversation, Mr. Jukes-Browne suggested my 

 submitting a short letter to the Geological Magazine, as the subject 

 might interest students ; but the more I looked at the matter the 

 more abstruse and cumbrous did it appear ; and, from past experience, 

 I doubted whether the inquiry would not be more attractive to chemists 

 than to geologists.'^ 



1 Hitherto we have been under the necessity of invoking the agency of percolating 

 water. 



2 My friend Dr. Home very kindly read the MS. of this paper, and he gives me 

 leave to say that he agrees with the views expressed in it. Indeed, I believe it would 

 be nearer the truth to say that he had come to similar conclusions before he saw my 

 MS., and had discussed them with my former colleagues of the Scottish Geological 

 Sm'vey. 



^ I was unaware at the time that quartz-veins were under discussion in the Magazine.. 



