290 T. W. E. DAVID. 
phism with development of white spots due probably to formations 
of chiastolitic minerals. The thin sills, from one-eighth of an 
inch up to about one foot, are greenish-grey in appearance, 
resembling quartz-diorites. The thicker sills, from over a foot up 
to several yards thick, have a more definite granitic aspect. In 
places where the sills have partly replaced fossiliferous crinoidal 
limestones, casts of the crinoid stems may be distinctly discerned 
in the granitic base of the sill. This obviously is the correct 
explanation of the apparent anomaly of the occurrence of fossils 
in the eruptive rocks at Hill End. 
The occurence of waterworn pebbles in the sills at the above 
locality and also at Emmaville is, I now think, undoubtedly due 
to the same cause. The sills of fine grained granite and quartz- 
porphyry have, when intruding the conglomerates, dissolved and 
assimilated the base of the conglomerates, but have not been able 
to digest the less soluble pebbles. This is the origin of the zone 
of waterworn pebbles, at Rose Valley, Emmaville, striking obliquely 
across the large quartz-porphyry dyke, and passing in either 
direction, as soon as it leaves the dyke, intoa typical sedimentary 
conglomerate. I would further suggest that the granitic bosses” 
of New England ete. are laccolitic in shape rather than conical. 
If they were conical it is hard to understand why they should not 
have had strength enough to uplift Lower Silurian, Cambrian, 
and Pre-Cambrian rocks, which would have subsequently been 
exposed at the surface through denudation. As a matter of fact 
the oldest sedimentary rocks in contact with the New England 
granite appear to be Upper Silurian. On the laccolitic hypothesis 
the absence of rocks older than Upper Silurian around the granite 
can be explained. Immense volumes of granite may have been 
squeezed through comparatively small punctures in the Pre- 
Silurian crust, so that the lifting power of the granite on the rocks 
forming the sides of these relatively small well-holes would be far 
less than it would be around the periphery of a cone, the area of 
the base of which would considerably exceed the area near the 
summit of the cone exposed by denudation at the earth’s surface. — 
