Colonel McMahon — Granite of the Himalayas. 219 



have been flattened to a wafer. A mere glance at the plate, a photo- 

 graph reproduced by the heliogravure process, will show this at once. 



Fifthly, neither the crypto- crystalline mica, nor the fish-roe quartz, 

 described ante, can possibly have been produced by the grinding 

 down of the mica and the quartz in the consolidated rock, or by any 

 analogous process ; for, besides the crypto-crystalline mica, and the 

 fish-roe quartz, we have very numerous large crystals of muscovite, 

 biotite, and quartz. The muscovite and biotite are large and beauti- 

 ful specimens of these minerals, and they orient in ail directions and 

 at every angle up to a right angle to the strings of crypto-crystalline 

 mica. Mechanical action potent enough to have reduced mica to the 

 pulpy condition of the crypto-crystalline mica would not have left the 

 larger micas untouched. Similarly, the fish-roe quartz not only fills 

 cracks in felspars, and forms a sort of setting to quartz grains, but 

 it meanders about in the interior of large quartz grains, and termi- 

 nates abruptly inside them, in a way that does not suggest to the 

 observer that he is looking at cracks stopped with micro-crystalline 

 quartz, but rather that the crystallization of the quartz was brought 

 to a comparatively rapid termination towards its close. 



Indeed, properly considered, I think the crypto-crystalline mica, 

 and the fish-roe quartz, furnish a clue to the riddle. I may mention 

 in passing that I have observed in a felsite patches of material closely 

 resembling the crypto-crystalline mica mixed up with the quartz and 

 the ordinary felsitic base ; but I desire more particularly to refer to 

 a series of rocks which occur in the peninsula of India about eighty- 

 five miles nearly due west of Delhi. We have there a very interest- 

 ing group ranging from felsites, quartz-porphyries, and granite-por- 

 phyries to almost true granites. The felsites appear to be true lavas ; 

 and the others, though merging gradually into rocks of plutonic 

 character, are probably more or less directly connected with them. 

 These rocks never show any trace of foliation, or give any indication 

 of crushing. But what is important to note is, that the gradual 

 genesis, so to speak, of the fish-roe quartz may be observed in these 

 rocks. The quartz gradually becomes more and more developed in 

 the felsitic base ; it begins to crystallize out in grains of microscopic 

 size, and the grains increase in number, until at last the whole base, 

 or ground-mass, of the granite-porphyries partakes closely of the 

 characters of the fish-roe quartz of the Dalhousie granite. The true 

 explanation of the foliation of the latter rock I believe to be briefly 

 as follows : — The rock had partially consolidated before it was moved 

 into place : large porphyritic crystals of felspar, and numerous micas 

 and quartz grains had formed ; it was very much in the condition of 

 a felspar-porphyry, or a granite- porphyry ; when, in the course of 

 the earth-movements that were contorting, crumpling, and folding 

 the strata of the Himalayas, this imperfectly consolidated granite- 

 porphyry was forced through the faults that had been formed along 

 the axes of over thrust-folds; the semi-plastic mass was subjected to 

 enormous pressure ; the mica was crumpled ; the crystals of felspar 

 were cracked and ruptured ; and so much of the micaceous siliceous 

 materials as remained unconsolidated were forced into the rents made 



