22 
MUSEUM BULLETIN NO. 2. 
( b ) The composite sills represent a simple magma later 
injected with the acid material coming either: — 
(1) directly from an intercrustal reservoir; 
(2) or from lower sills in which any of the things listed 
under 2a may have happened. 
It is believed that the simple and composite sills are mag- 
matically related, for, if they belonged to distinct intrusions, 
one would expect to find some evidence of this in the field. 
But such has not been found, though the simple and composite 
sills occur in the same sections and have been examined in many 
places over a very wide area. Also the gabbro in both types 
is identical in composition and all gradations occur between the 
gabbro and the granite (micropegmatite). The rock types are 
analogous to the extrusive phases — the Purcell Lava — and as 
both acid and basic lavas occur closely associated, it is evident 
that they are genetically related. Hence, it is concluded with 
some degree of certainty that the two varieties of sills are 
magmatically related. 
That such an intrusion of related acid and basic magmas is 
possible, is supported by the relations existing between the 
Buttermere and Ennerdale Granophyr of England. 1 In the 
Buttermere and Ennerdale districts occur intrusions of dolerite 
and granophyr into slates and volcanics. A point of resemblance 
between the phenomena exhibited in the two districts arises in 
connexion with the dolerite which precedes the granophyr in 
time of intrusion and which contains towards the centre of the 
mass, numerous pink patches of acid material which strongly 
resemble the main mass of the intrusive granophyr. Rastall 
supposes that the pink patches in the dolerite are a Mixture 
Rock and the following extract is quoted from his paper. 2 
“According to this, the basic dolerite was first intruded, and while 
still hot and partly liquid in the middle, another intrusion of more acid 
character took place from the same reservoir and penetrated into the still unconsol- 
idated centre of the earlier intrusion producing a hybrid rock intermediate between 
the granophyr and dolerite.” 
As already stated, Rastall has strong evidence that the two 
main intrusions of dolerite and granophyr are magmatically 
related. 
l R. H. Rastall, Q. J. G. S., vol. 62, 1906, p. 253. 
2 Ibid p. 263. 
