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interesting of the series. It crosses Gun Rock and all the 
ledges to the east, increasing in width from 3 to 4.5 feet. On 
the summit of Gun Rock it makes a clear intersection of the 
quartz vein just described, without faulting it. Throughout 
its entire extent this dike has the appearance of being very 
coarsely porphyritic along a zone from six inches to a foot wide, 
between the middle of the dike and the south wall. Careful 
examination shows, however, that it is not truly porphyritic, 
but what appear to be indigenous feldspars are really angular 
fragments of a coarsely crystalline feldspathic rock which is, 
apparently, partly granite but mainly syenite. The fragments 
range from the smallest size up to six inches or more in length ; 
and their true character is most obvious on the eastern ledge 
(Fig. 14). Dike 11 presents the same feature for a part of its 
sourse. The enclosed fragments in this dike are chiefly coarse 
granite ; and they begin very abruptly at a point about 20 feet 
from the intersection of the double dike and the same distance 
from the shore. They are of all sizes up to six inches and, as 
in 12, are crowded in a layer from 6 to 12 inches wide between the 
middle and south wall of the dike. Although no granitic rocks 
are developed on the surface nearer to Gun Rock than Jerusa- 
lem Road, the inference is irresistible that they actually under- 
lie Gun Rock; and the restricted distribution of the frag- 
ments in the dikes is a very plain indication that the upward 
movement of the melted rock in these fissures had nearly 
ceased before the underlying granitic rocks were sufficiently 
disintegrated to yield this debris. 
The intersection of the quartz vein on Gun Rock by a dike 
of the second system, and its perfect parallelism with the dikes 
of the first system, show that it probably dates from the form- 
ation of the first system, or else from some period between 
the two systems. South of this vein is another, smaller and 
parallel with it, but not observed to meet any of the dikes. 
Under the Park House on the summit of Centre Hill are two 
OCCAS, PAPERS B. 8, N. II. IV. 8. 
