REV. E. HILL ON THE ROCKS OF GUERNSEY. 419 
seems to be some tendency to a dip at right angles to the folds ; but the 
most marked feature is the general northerly and, therefore; inland 
dip. Possibly the character of the coast may have some connexion 
with this. 
| 7. GuneraL Remarks, 
Although I have no doubt as to the Archean character of the 
Guernsey gneiss, yet absolute proof is wanting at present, and may 
perhaps never be obtained. It is possible that when Jersey shall have 
been satisfactorily worked out, some evidence may be forthcoming. 
There is a mass of diorite there on the shore at Greve d’Azette, east 
of St. Heliers, which closely resembles the dioritic intrusions into 
the gneiss at Fermain Bay. Again, the great crystalline masses 
which form three out of the four corners of Jersey remind me much 
of the Cobo granite. No gneiss, however, is known in any Channel 
Island except Guernsey and Sark*. 
The relative ages of the rock-masses are fairly clear. The gneiss 
is no doubt the oldest. The ‘‘ Birdseye” (hornblende-gabbro) is almost 
certainly next ; indeed, unless we can identify the Bon Repos rock 
with it, we have no ocular evidence that it is later than the gneiss. 
The diorites certainly cut the gneiss, and almost certainly cut the 
“‘ Birdseye” also. The granites are the latest of the more important, 
groups; but Ido not know their relations to each other. To arrange 
the dykes in chronological order would require much more time and 
attention than I have been able to give. Intersections are frequent 
enough, so that the materials exist ; thus on the shore by Hougue a 
la Perre battery the “ Birdseye” is cut by thin white dioritic dykes, 
while a broader black hornblendic band cuts right across them both. I 
fancy that the coarsest dioritic dykes are earliest, and contemporary 
with the diorite group; the less coarse greenstones next; the 
granitic dykes later still; and the compactest greenstones posterior 
to all. The mica-traps are, no doubt, late; their age may be the 
same as those known to exist on the mainland. The pink felsites 
of Castle Cornet resemble certain rocks of Jersey, and are probably 
also among the later intrusions. 
The area occupied in north Guernsey exclusively by igneous rocks 
is, as may be seen from what has been said, very large, not less than 
six square miles; and whenever the outlying reefs are properly 
examined it will probably be found much larger. 
Perhaps the most interesting feature of these rocks is the extent 
to which a structure tending towards that of schist has been 
developed in them by subsequent action. ‘There can be little doubt 
that the agent has been pressure. Pressure, we know, can produce 
such effects, and the rolling and faulting of the gneiss show that 
pressure has been at work. Granite has had a gneissose aspect im- 
parted to it; diorite has had slaty bands developed in it; greenstone 
dykes have been reduced to the condition of schist or slate. The hke 
may therefore have happened in other localities. Two miles to the east 
* Prof. Liveing has published geological sketch maps of Sark and Jersey in 
~ Cambr. Phil. Soc. Proce. vol. iv., and the account of Sark there is good. 
