Col. McMahon— Granite of the Himalayas. 63 
these porphyritic lavas,” writes Professor Judd with reference to 
a somewhat different class of rock in his well-known work on 
Volcanoes, p. 256, “points to the conclusion that while the crystals 
in their ground-mass have separated from the liquefied materials 
near the surface, the large embedded crystals have floated up from 
ereat depths within the earth’s crust, where they had originally 
formed.” I do not mean to affirm that a similar inference would be 
safe in respect of all porphyritic rocks, plutonic as well as volcanic ; 
but I think we may safely draw that inference with regard to the 
porphyritic crystals in the Dalhousie rock, for in some places tongues, 
and veins, intruded into the adjacent schists are as distinctly por- 
phyritic as the main mass of the granite (Records Geol. Surv. India, 
vol. xv. p. 45), and I do not think any one would allege that the 
large porphyritic crystals in the small veins were formed i situ. 
The same conclusion must, I think, be arrived at when large porphyritic 
crystals are found (Records Geol. Surv. India, vol. xvi. p. 129) in 
a matrix so fine grained that the Dalhousie rock occasionally assumes 
the superficial appearance of a felspar porphyry. 
That the granite was, at the time of intrusion, partially cooled 
and imperfectly viscid, is almost conclusively proved by the con- 
dition of the foreign fragments included in it. At page 175 
of the volume to which Mr. Oldham has referred (vol. xvii. of 
1884) I wrote as follows:—‘In the case of the long splinter of 
schist, a fragment of which is depicted in the plate attached to this 
paper, it is clear that it must have been included in the granite 
when the latter was already partially consolidated, and had lost 
a considerable part of its heat. JI have found on other grounds, in 
my previous papers, that the gneissose-granite had partially con- 
solidated before it was intruded into the stratified rocks; and the 
evidence afforded by the fragment of schist under consideration con- 
firms this conclusion. The schist would not have retained its fine 
foliation had the granite been in a fluid state, and at the high heat 
indicated by that condition.” The reasons for coming to this con- 
clusion are given in detail in my paper. 
I may note in passing that the texture of the porphyritic granite 
immediately round the fragment of schist referred to is fairly granitic, 
and this fragment proves that the rock from which it was torn was 
in a foliated condition before the intrusion of the granite took place. 
The granitic structure of the granite compared with the fine foliation 
of the schist, a point that is well brought out by the heliogravure 
reproduction of a photograph given at p. 175, vol. xvii. Records 
Geol. Surv. India, appears to negative the assumption that the folia- 
tion of the Dalhousie granite and the foliation of the schists into, 
and through which, it was intruded, are both alike due to pressure- 
metamorphism operating after the intrusion of the granite. 
From the use of the words “still heated granite,” and from the 
context, ] am under the impression that Mr. Oldham is of opinion 
that the structural changes in the granite which resulted in folia- 
tion were produced before it had perfectly cooled down after its 
injection; if so, our views seem to be substantially identical. 
