MICROPEGMATITE IN PURCELL SILLS. 
23 
Another explanation of the occurrence of the pink spots in 
the dolerite might be given. They may represent the results of 
differentiation subsequent to intrusion by which the dolerite 
was finally freed from the granophyr and hence would be syn- 
genetic. Many cases of such segregations are known in all parts 
of the world, and in general, in such cases, no granitic intrusion 
subsequent to the dolerite is known. In the description of the 
geology of the Antarctic 1 are noted numerous sills of gabbro 
intruded into sandstones. The interior of the sills contains 
patches of micropegmatite and quartz. The contact of the 
gabbro and the sandstone is fine grained and less acid than the 
interior of the sill. Here the acid patches are original, for no 
intrusion of granite subsequent to the gabbro is known. Hol- 
land 2 tells of augite diorites in southern India, which contain 
segregations of micropegmatite, and he considers that 'this acid 
material might have been separated from the augite diorite and 
injected as separate intrusions, similar to the phenomena and 
relations exhibited at Carrock Fell . 3 
% 
Since from the above discussion, it is seen that the evidence 
supports the view that the simple and composite sills are mag- 
matically related, the granite (micropegmatite) in the composite 
sills might be a separate intrusion of granite into simple sills. 
In this case, the sill would be compound. Under this suppos- 
ition the second intrusion of granite (micropegmatite), since it 
occurs in some of the sills only and then always towards the upper 
margin, would be selective in character, which of itself is some- 
what difficult of explanation. But there is also a complete lack 
of any evidence of cutting and no feeders (dykes) of acid material 
were observed, though basic dykes, the feeders of the basic 
sills, were observed. Furthermore, the contact of the gabbro 
and granite (micropegmatite) is in all cases gradational and the 
stratiform arrangement of the materials in the sill does not favour 
this idea. 
Therefore, by the process of elimination, it may be concluded 
that the composite type differentiated in place and that it 
1 National Antarctic Expedition, 1901-1904, vol. 1. 
2 Holland, Q. J. G. S., vol. 51, 1895, p. 125. 
8 A. Harker, Q. J. G. S. vol. 50, 1894, p. 311. 
Q. J. G. S. vol 51, 1895, p. 125. 
