352 Lieut.- General C, A. McMahon — 



The above description of the peti'ographic characters of the Scotch 

 rock LQight be applied word for word to the Himalayan granite. It 

 is gratifying to be able to point to the independent evidence of an 

 expert who shows that it is "highly probable" that the pressure 

 which produced the foliation of a Scotch granite "acted before tbe 

 rock-mass had actually cooled." It further appears from Mr. Teall's 

 remarks that the granite was in a partially consolidated state whea 

 the pressure was applied. " The last constituents to solidify," he 

 writes, " are those which have yielded most to the deforming 

 stresses"; and the pressure applied to the uncooled and partially 

 solidified rock crushed the quartz and felspar crystals to such 

 an extent that they passed " into micro-crj^stalline and crypto- 

 crystalline streaks," We get "flaser" structure, and, in the words 

 of Mr. Home (p. 25), "The quartz and alkali-felspar are the con- 

 stituents which yielded most readily to dynamic agencies. The 

 yielding of these constituents dragged out the biotite and horn- 

 blende." The correspondence of the Scotch and Himalayan rocks 

 in the origin of their foliation, and in their crush and flaser 

 structures, would seem to be complete ; and the testimony of Messrs. 

 Home and Teall to the effect that these structures, in the case of 

 the Scotch granite described in the above Memoir, were probably 

 produced whilst it was still uncooled and incompletely solidified, 

 is all the more important as these observers have been by no means 

 unfavourable to the cause of dynamo-metamorphism. 



If, then, we can get "flaser" structure, and the crushing and 

 dragging out of minerals into streaks by pressure applied to an 

 igneous rock prior to its complete cooling and solidification, it seems 

 to me simply nonsense to appeal to flaser structure, crushing, and 

 the dragging out of minerals, as conclusive evidence that the rock 

 exhibiting these structures has been deformed after its consolidation. 

 Those who wish to establish that conclusion for any particular 

 igneous rock must produce good and convincing evidence to prove 

 that the dynamic movements took effect after, and not hefore, its 

 consolidation. 



The condition of mind of those who think that it is only necessary 

 to produce evidence of crushing to close controversy on the point at 

 issue, reminds me of those who, in days gone by, exclaimed with 

 enthusiasm as they stood gazing at a gabbro : " We know for 

 certain that this is a metamorphosed sedimentary rock, because it is 

 foliated !" Lest any should think this statement exaggerated I will 

 give extracts from a recently published memoir (60th Eeport, 

 U.S. Geol. Surv. 1894-5), "On the Principles of North 

 American Pre - Cambrian Geology," by Mr. C. E. Van Hise. 

 " A few years ago," he writes, " it was assumed as a matter of course 

 that distinct lamination in the gneissose granites, gneisses, and 

 schists, and the fact that these rocks were believed to grade into 

 the elastics, were taken as conclusive evidence of the original 

 sedimentary origin of the whole " (p. 748) ; and the author refers 

 by name to five authors who, among others, actually acted on the 

 above-mentioned principle. Van Hise also points out (p. 768). 



