412 REV. E. HILL ON THE ROCKS OF GUERNSEY. 
cannot be settled so decisively as for the diorites and syenites. The 
junction with the surrounding rocks affords evidence only in support 
of the igneous nature of those. Asin the case of the last group, 
the quarries and the rocks of the shore do not in general show 
satisfactory signs of bedding. So too the distribution of the varieties 
over their area does not suggest a derivation from varying series of 
sedimentary beds. But they do in more than one place present 
appearances that very closely resemble remnants of stratification. 
On the shore at Hougue a la Perre, in the spotted rock described 
above, well-marked alternate layers of whiter and darker rock slope 
gently to the south-west. At the north end of Bellegreve Bay exactly 
similar appearances in the same peculiar variety of rock dip similarly 
in the same direction. In the quarry on the south side of Delancey 
Hill a similar banding may be noticed, but seems to dip steeply to 
the north. It cannot be examined, as the quarry floor is occupied by 
water*. However, I do not feel satisfied that any of these bands 
really represent beds. They are absent from the group in general, 
and even from other parts of the outcrops in which they occur. The 
rock does not at all resemble a metamorphic rock. Professor Bonney 
concludes from the microscopic examination that this group also is 
igneous. Though their boundary affords no evidence, there are rocks 
intrusive into the gneiss at Bon Repos Bay which consist mainly of 
hornblende and bear some resemblance to some of this group. I 
have caused analyses to be made of the Bon Repos rock and of a 
specimen of hornblende-gabbro from Hougue a la Perre. The 
results show considerable resemblance. 
Hougue a Bon Repos 
la Perre. 
alice. & oreo bo Aire Sees, Sait 45°82 45°28 
Adprin |) ob dane 2ae Stents ee 14-06 20°50 
Herrig Oxi] .:20) 5 secs. wae. 24°52 22°25 
EINE oon ogo an agen ear eee sees: 4°52 5°58 
Mapnesia i2.52.22,5. Sister nese 4°31 3°00 
Loss by ignition 22.84.2202 ‘97 1-00 
94:20 97°61 
5. Tur GRANITES. 
Granitic dykes occur at many points along the coast. These, 
however, will be mentioned in the next section. Here our concern 
is with such rocks as occupy considerable areas, areas that may claim 
recognition on a map. 
Foremost among these comes the granite of Cobo. This beautiful 
variety extends along the shore of Cobo Bay, and northward as far 
as the bay called Portinfer, while on the south it forms the whole 
of the peninsula on which stand the Hommet barracks. Its boun- 
dary inland is very irregular, but is seldom more than a quarter of 
a mile back from the shore. It is usually so decomposed that good 
specimens are hard to get. This is no doubt the reason why it isso 
little used for building. A quarry not far from the Cobo Hotel is 
* T have shown, in Cambr. Phil. Soc. Proc. iv. p. 385, that the bed of stratified 
quartzite said to occur in this quarry is really a dyke. 
