
TRANSACTIONS OF THE SECTIONS. 51 
In the red granites I observed one set of planes running nearly north and south, 
‘with a dip to the west and a cross set east and north, and which had a dip north. 
Hornblende is not absent in the second group of crystalline rocks, as an occasional 
constituent; and in these cases, as in St. Sampson’s parish, it makes its appearance 
by gradual increase, and as it were by passage from one rock to another. 
The third group is quite distinct: the different appearances which it assumes, from 
the preponderance of one or other of its constituents, would cause it to be described 
mineralogically under a great variety of names. I noticed, however, a single dyke in 
the island of Jersey which in one place was an earthy hornblende (wacke), then com- 
pact greenstone trap, hornblende with distinct crystals of felspar; lastly, hornblende, 
with large plates of mica. 
The intrusion of the hornblendic series is of subsequent date to that of the granitic 
rocks : as to the period in the geological scale at which this took place, it would be 
hazardous to conjecture; they have broken up and been projected amongst the gra- 
nites, in the same manner as we have seen that the granites affected the slate rocks. 
A vast lapse of time must have been required for the cooling down of the fluid gra- 
nitic masses; yet it is evident that the whole of that structure of divisional planes was 
complete before the intrusion of the sienitic rocks; an illustration of this represented 
the dyke in every instance following one of these sets of planes. But for nume- 
rous other sections, where the granite is seen caught up in the greenstone in great 
angular masses, it might be supposed that the two rocks were arranged in parallel 
beds; instances of the subsequent date of the hornblende series is perhaps best seen 
in Jersey, but good examples are to be found in Guernsey. 
At several places in this same island is to be seen a deposit of fine sedimentary 
matter, conforming to the irregular surface of rock on which it rests. These accumu- 
lations have for afew years past been worked for the purposes of brick-making, so that 
good sections can be obtained. Their position is on the high table-lands of the south 
part of the island, so that at the time of their deposition the whole must have been 
submerged ; but besides this, the beds themselves would indicate a great depth of 
water. No fossils that I could ascertain have ever been met with. In one or two of 
the lower portions of this deposit, and where the sands were rather coarser, I detected 
fine sharp angular fragments of chalk flints ; and guided by many considerations which 
it would be needless to mention here, but which will readily suggest themselves to 
those acquainted with the geology of the south-west parts of France, it seemed to me 
that these beds might be outlying patches of the deep sea eocene period. 
The geological phenomena of these islands next in date are referable to sub-aérial 
conditions—the deep disintegration of the crystalline rocks, and the accumulation of 
the materials so produced. The thickness of these accumulations indicate a long lapse 
_ of time; they cover not only all portions of the larger islands, but are found capping 
_ the smaller groups of rocks which surround them: they come down to the present 
sea-level; they evidently, by their position, belong to a period when the whole of 
_ those islands had a much greater amount of elevation than at present. 
The old peat-beds and forest-trees of Catel parish belong to this period of sub-aérial 
_ conditions, as do also the submerged forests which run out from these islands at so 
many places, Vason Bay, Grand Cobo. 
The elevation of the whole of this group at this line was probably very consider- 
able. 
Up to a height of no great amount above the sea, the surface is covered by an ac- 
cumulation of sharp sand, with occasional lines of shingle; chalk flints enter largely 
into the composition of this. In the parish of St. Sampson it will be seen resting on 
_ the surface of the granite, as in many of the quarries; but it occurs equally on the sub- 
| aerial beds; the thickness of these accumulations is very trifling, and can only indi- 
cate a depression beneath the present level of very transient duration. In the Island 
of Jersey such lines of inland cliff as that which extends from Gorey southwards, at 
_ the base of which lie the ancient marine beds, covered along the sea-bord with blown 
—, would indicate a rather lengthened period of stability before the last change of 
level. 
_ Such is the series of physical change which this group of islands appears to have 
undergone; its geological history is simple compared with many other districts, but 
for the apparent fact that it should have preserved tracts as dry land through so many 
surrounding changes, and probably since the post-eocene period, 
. 4c 
