236 Correspondence — Mr. C. Fox Strangways — Prof. Sidl. 



As for the Piora schists, I am sorry to have misunderstood Dr. 

 Stapflf, but think he would have done better to refer to my letter as 

 published in the Geological Magazine (1892, p. 90) instead of to 

 an abstract of it, necessarily condensed. He will find my words to 

 be " If I am right in understanding Dr. Stapif to assign the Piora 

 schists to the Carboniferous system," etc. The fact is that I had 

 great difficulty in coming to a conclusion both as to the exact 

 position of the divisions which he had drawn in his published 

 sections and paper, and as to how much was covered by the 

 terms which he employed. The terminology of petrologists at 

 present is rather unsettled, so that we do not seldom find difficulties 

 of this kind arising in regard to details. But if the Piora schists 

 are part of a series extending " from the Carboniferous to the 

 Jurassic age," I fear that I must leave the remainder of the sentence 

 partly quoted at the top of page 160 otherwise unaltered. 



My remark as to the inadequacy of photographs to decide whether 

 organisms occurred in the Altkirche marble applies equally to the 

 " sand grains " in the Guspis gneiss. That a gneiss may be of 

 sedimentary origin I do not deny, but I doubt whether it would 

 be possible to recognize with certainty the original clastic grains, 

 unless they had been so large as to make this term inappropriate. 

 For instance, I have examined many quartz-schists, in which I 

 suspected certain grains to indicate the position of original con- 

 stituents, but have met with only one case which I felt would 

 satisfy a sceptic (discovered by Mr. J. Eccles last summer), and here 

 they were pebbles rather than grains. But I have seen many cases 

 where a structure, due to the crushing of a crystalline rock, wonder- 

 fully simulates that of an ordinary clastic rock, so, as I have been 

 more than once led into error in this matter, the proverb holds 

 good, " once bit, twice shy." T. G. Bojsney. 



DR. ALEX. BROWN ON SOLENOPORA. 

 Sir, — In Dr. Brown's article on the structure of Solenopora there 

 is a slight error in the horizon given for the Yorkshire specimens 

 which should be corrected, especially as the rock in question was 

 for some time considered to be the equivalent of the Great Oolite. 

 The Malton specimens are obtained from the Corallian, and they 

 are also very abundant throughout the Ayton-Brompton Coral Eag. 



Geological Survey, C. Fox StrANGWAYS. 



Leicester. 



MR. WATTS' S PAPER ON THE TARDREE PERLITE. 

 Sir, — On thinking over the subject of Mr. Watts's interesting 

 paper read before the Geological Society on March 21st last, in 

 which he endeavoured to prove — by means of very beautiful 

 magnified sections of the Tardree trachyte — that the perlitic 

 structure is sometimes continued from the glassy magma into the 

 enclosed crystals of quartz, it seems to me that the essentially 

 distinct molecular structure of the two mineral substances was not 

 sufficiently taken into account, and that it is only on a recognition 



