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BEV. E. HILL ON THE ROCKS OF GUERNSEY. 415 
Grand Havre, on its east side in some of the quarries on Mont 
Cuet and Grand Camp, in a knoll by the road south of Lancresse 
Common, and, I think, in someof the quarries east of Vale. It is 
distinguished by the size of its crystals, which are usually about -2 
inch in diameter, by the size and perfect shape of its black 
mica, and by the presence of abundant and well-crystallized horn- 
blende. My specimen from the knoll is rather decomposed, and 
shows less mica than the others, and little quartz. On Mont Cuet 
this is mixed up with a dark finely crystalline micaceous rock in a 
very curious way. The junctions seem scarcely sharp enough for 
intrusions ; the absence of any trace of fissuring seems to exclude 
metamorphism along cracks or joints ; the shape and arrangement of 
the patches show clearly that they are not included fragments or 
breccias. They remind me most of nodes or segregations, but I have 
never before seen these of such a size and degree of complication. 
Is it possible that the mass when just solidified or solidifying became 
subjected to stresses which did not actually rupture the rock, but 
only caused crystallization to go on differently in the parts where 
the strains came? A very similar relation between a white granite 
rock and a fine-grained dark mica-syenite occurs in two quarries 
west of Vale church, and is also thought by Prof. Bonney (see 
appendix, p. 422) to be the boundary of anode. Here, however, the 
white granite is that which veins the parent dark micaceous rock. 
What would be the nature of the subsequent junctions if a super- 
heated molten rock has forced its way through an igneous mass still 
nearly at the temperature of fusion? Will not this be again raised 
to the melting-point, and in parts be absorbed into the new comer, 
in others have a recrystallization along the contacts, and an interpene- 
tration of constituents with the other? I suspect that this may be 
the cause of some of these phenomena. 
A beautiful white crystalline rock consisting of quartz, felspar, 
mica, and hornblende, forms a large part of the great quarry west 
of the spot called on the map Baubigny Mill. This rock has a 
curious appearance of cleavage. The rest of the quarry is in a rock 
of the hornblende-gabbro group with huge secondary crystals of 
hornblende. Another rock of granitic affinities occurs at two or 
more spots on the west boundary of the above group, in the neigh- 
bourhood of Hougue Nicolle. The rare and imperfect exposures in 
this central part of the island offer little hope that the nature and 
relations of these rocks will ever be fully made out. 
Besides the varieties here mentioned, several quarries afford rocks 
which contain quartz in larger or smaller quantity. Some of these 
may be true granites, while others seem rather quartz-diorites, and 
are probably only varieties of the dioritic group, with an unusual 
amount of silica. Sometimes a granitic material occurs veining an 
ordinary blue diorite, in the same manner as the mica-syenite of 
_ Vale, as in a quarry by a dark square tower above Les Genats Road. 
_ Very seldom is a rock actively quarried which contains any large 
amount of quartz. We find rock that may be classed with the 
granites in many abandoned excavations; but the windmill which 
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whe aes 
> o_ Se 2. 
