IV. — Supplementary Remarks on Quartz Rock, 

 By JOHN IVrCULLOCH, m.d. f.l.s. 



CHEMIST TO THE ORDNANCE ; LECTURER ON CHEMISTRY AT THE ROYAL MILITARY 

 ACADEMY ; AND GEOLOGIST TO THE TRIGONOMETRICAL SURVEY. 



[Read November 3, 1819.] 



JLlAVING on two former occasions continued the imperfect history of 

 Quartz Rock^ originally given in the second volume of the Society's Trans- 

 actions, as fresh materials occurred, no apology is required for this additional 

 notice, the result of some investigations made during the present summer 

 (1817). It is not necessary to enter into further details respecting its geo- 

 graphical extent in Scotland, although large additions might be made to the 

 tracts which were described as composed of it; the principal objects of the 

 former communications having been already attained in the proofs adduced of 

 its importance as a member of the primary stratified rocks. The present 

 remarks relate solely to the geological relations of quartz rock; and their 

 object is to confirm and extend some circumstances respecting those which, 

 although formerly mentioned, were either too limited to be quite satisfactory, 

 or were attended with some degree of obscurity. 



The relations of quartz rock to micaceous schist, to argillaceous schist, and 

 to graywacke, have been fully described in the former papers. At the same 

 time it has been observed, that it graduated on some occasions into gneiss, 

 and also alternated with certain varieties of that rock, as well as with the 

 micaceous schist Avhich accompanied it. But as the gneiss in these cases was 

 of an indeterminate, and, perhaps, of a disputable character, while it seemed 

 rather a modification or a subordinate member of the micaceous schist, than 

 an extensive and independent mass, it still remained a doubt whether quartz 

 rock did actually alternate with gneiss in an unquestionable manner, and on a 

 scale corresponding to its alternation with micaceous schist. That doubt has 

 now been removed by a further examination of the west coast of Sutherland, 

 where it abounds; as I formerly mentioned in the original communication on 

 this subject. 



