280 Correspondence. 



I liad, however, far too great a respect for the many eminent 

 geologists of Scotland, and too little confidence in either Mr. James 

 Geikie's petrology, or his assertions, to accept the ahove statement 

 without examining into its correctness, and I think the result of the 

 inquiry will satisfy the public that the name of the Scottish geologists 

 has been taken in vain, and that 



1. The term "greywacke," when "familiar to," and "used by" 



Scottish geologists, corresponds satisfactorily with the definition 

 I have accorded to it — one endorsed by geologists of all nations. 



2. That this rock possesses not only a distinct mineral character, 



but, within certain limits, also a definite chemical composition. 



3. That quartz is " a necessarily preponderating ingredient," and is 



generally present in fully seventy-five per cent. 



4. That the term is not, by Scottish geologists, "' exclusively applied 



to felspathic," etc., nor that the word "felspathic" should be 

 at all used when referring to normal " greywacke." 

 Mr. James Geikie, who in. his reply expresses his doubt as to my 

 " careful examination of the literature of the subject," will think it 

 still more strange and presumptuous in my thus attacking him at 

 home, and undertaking the defence of the Scottish geologists ; but I 

 would ask him whether he is aware that it was a Scottish geologist, 

 Professor Jameson of Edinburgh, the pupil and friend of Werner, 

 "who first introduced the term " greywacke " into the English scien- 

 tific language ; and if he will refer to that author's work upon the 

 mineralogy of the Scottish Isles, published in 1800, he will there 

 find (vol. i. p. 226) my deimition perfectly confirmed. If, then, he 

 turns to the (for its period, excellent) work on petrology, "Mac- 

 culloch's Classification of Eocks," published in 1821, also by a 

 Scottish geologist, it will be seen, at page 358, that the difierent 

 varieties of greywacke are there respectively defined as rocks 

 composed of — 



1. " Quartz sand, intermixed with lamina or massive schist." 



2. " Quartz gravel, of various sizes, similarly intermixed." 



3. " Argillaceous schist, with very fine grains or powder of quartz. 



Not fissile ; fracture sometimes rough and splintery, and often 

 resembling the fine and gi'ey varieties of primary sandstone." 



4. Ditto, "with visible grains of quartz of various sizes, and re- 



sembling the coarser varieties of the same rock." 

 And if, to carry the literature of the subject down to the present 

 day, he refers to a recent work, also Scottish, and which he already 

 has quoted in his reply, viz., Page's Advanced Text-book of Geology, 

 he will there find (p. 309) the previous descriptions confirmed — 

 nor in any case will he find the felspathic element of greywacke, 

 which is so convenient for his metamorphic hypothesis, even alluded 

 to by these Scottish geologists, David Foebes. 



London, Zrd April, 1867. 



