406 REV. E. HILL ON THE ROCKS OF GUERNSEY. 
cliffs, from Moulin Huet to Torteval; along the east coast it is 
somewhat less coarse, occasionally containing granitoid beds, of 
finer material and often hard to distinguish from dykes; but even 
at its edge, round Castle Cornet, the aggregates are half an inch 
long. On the west coast also it maintains a similar character 
up to its boundary. But this coarseness is not universal. Along 
_ Perrelle Bay occurs a rock of very different character. It is bluish 
within, weathering white, and consisting of crystals which are seldom 
longer than one eighth of an inch. Its constituents are felspar and 
hornblende, rather well crystallized; it contains many dark oval 
nodes a foot or more in length*; and it has the massive appearance 
and jointing of an igneous rock. That it is notigneous is, however, 
shown both by a well-marked structure which it possesses, and by 
its gradual change as we trace it along the shores of Lerée Bay and 
the isthmus of Chapelle Domhue into the porphyritic gneiss of Lerée. 
A rock almost undistinguishable from this occurs also in a quarry 
near the brickfield at the east end of Les Talbots Road. In another 
quarry, some three hundred yards to the south of this, the rock is as 
fine-grained as an ordinary sandstone—a dark micaceous rock with 
well-marked banding and little cleavage. This variety I have not 
discovered elsewhere. 
One locality deserves especial notice. This is the little peninsula 
in Rocquaine Bay, on which stands a fort called on Grigg’s map 
Rocquaine Castle, but on the Admiralty Chart, Fort Grey. Here, 
interstratified with the ordinary gneiss of the locality, are several 
beds of what seems to be slate, and slate by no means highly metamor- 
phosed. This rock attracted the attention of the earliest observer, 
Macculloch, and is certainly that mentioned by Ansted as “ a patch of 
clay-slate in Rocquaine Bay.” It is difficult to believe that these beds 
have experienced the same agencies of alteration as the coarse crystal- 
line gneiss of Moulin Huet and Petit Bot. They are obviously true 
intercalations; they cannot possibly be nipped-up pieces of an overlying 
formation. I doubted at one time whether the rock in which they 
occur was the normal rock of the neighbourhood ; but subsequent 
examination seemed to render this certain. It is, however, variable in 
nature, and some which outwardly seems normal gneiss, within proves 
to be a similar slaty rock containing patches or pockets of coarser 
materials, and nodules 7 or 4 inch in long diameter of clear granular 
quartz. The finer beds are much crushed and nipped up; but the 
general strike and dip of all is N.—S. and vertical, agreeing in these 
with the other indications of the region. 
What then is the history of these rocks, so exceptional in cha- 
racter? They cannot be, as at one time I conjectured, later beds, a 
sort of arkose of gneiss; for they seem to occur in conformable 
succession. It has been suggested to me that they may be dykes ; 
and, slaty though they look, there are in Guernsey dykes as slaty. 
* These nodes in a non-igneous rock are curious. Are they of material 
originally peculiar, or are they the result of some fragment of matter which 
has produced chemical change in the rock around it? Some similar phenomena 
in the upper gneiss of Sark rather suggest the former interpretation. 
