480 Correspondence — Mr. John Young. 



were very helpful in illustrating those of the Start district. So, 

 with a greatly enlai'ged experience, both in the field and with the 

 microscope, I could now improve my former paper {e.g. I could 

 amend the accounts of the "chloritic " rocks ; should be more ready 

 to recognise altered basic igneous rocks among them ; should say 

 that the mineral, very doubtfully identified with kyanite, and some 

 of the smaller grains of water-clear mineral — thought then to be 

 quartz — were more probably secondary felspars), but I should 

 express myself, if possible, yet more confidently as to the distinction 

 in lithological characters and geological age of the two groups of 

 rocks, the schists and the slaty Devonian system. 



Mr. Hunt, so far as I can judge from internal evidence, has had 

 little experience in dealing with problems such, as that which 

 he attempts — perhaps the most difficult j^resented to petrologists. 

 Possibly his experience may be commensurate with my own, but 

 till I have reason to believe that he has studied such problems in 

 other fields than Sonth Devon, and has ample materials at his 

 command for the necessary research, I must decline to do more 

 than say that my original opinion is not in any way altered by his 

 dissertation. 



T. G. Bonnet. 



" CONE-IN-CONE STEUCTUEE." 

 Sir, — In the September Number of the Geological Magazine 

 there is a note by W. S. Gresley, on " Cone-in-cone Structure," in 

 which he refers to " Mr. John Young's theory of how the rock was 

 formed." With your kind permission, I beg to state, that I have no 

 " theory " on the above subject, and in connection with the explana- 

 tions that I have given of the cone structure in my paper,' the word 

 " theory " is never used in any of my own explanations, but it will 

 be found on p. 25, where I give the opinion of Professor Newberry, 

 who there uses the word " theory " in connection with cone forma- 

 tion, " and the upwai'd escape of gases through a pasty medium." 

 Regarding its formation, all the explanations that I have ventured to 

 give are founded upon what is revealed in the best preserved, and 

 most illustrative specimens of the cone structure that I have found 

 in the carboniferous strata of the West of Scotland, and, I do not 

 think, that in these explanations of the various points of structure, 

 that I have stated anything beyond what the specimens themselves 

 most clearly reveal. I have, in various parts of my paper, pointed 

 out that there are structures which have been referred to " cone-in- 

 cone," but which present appearances so dissimilar to those noticed 

 in my paper, that to them my explanations do not apply, stating, 

 that they will each " have to be described with reference to their 

 external characters and internal structures." j^gj^ Young F.G.S. 

 HuNTEEiAN Museum, University, Glasgoav. 



1 Trans. Geol. Soc. Glasgow, vol. viii. 



