ON THE ROCKS OF GUERNSEY. 429 
heated, but experienced pressure from more than one direction, 
which would cause the parallelism of the gneissose structure to be 
interfered with by throwing the crystals out of their schistose 
arrangement, so as to form the confused structure of a granitic rock. 
If this were possible, the gneiss and syenite might both be meta- 
morphic. In Guernsey he would suggest that under the strain 
which the rocks had experienced in contortion, and while their 
materials were still in what might conveniently be termed a plastic 
state, the rock materials of fae island had been faulted, with a 
downthrow to the south, so that the gneiss had been brought into 
juxtaposition with the syenite. The slip need not have been great 
in amount for subsequent denudation to have laid bare the rocks in 
the positions which the author had described. The speaker would 
ask whether the specimen exhibited, which appeared to include a 
junction between stratified and igneous rocks, might not rather be 
due to a minor fracture in a semiplastic rock, and be partly the 
consequence of foliated structure developed parallel to the fracture, 
and partly of the nature of a veinstone. He considered that the 
remarkable development of schistose structure in the rocks which 
the author termed igneous, and which, like all schistose structure, 
must be attributed to pressure, was strong evidence in favour of the 
gneiss and syenite being contemporaneous, and favoured his con- 
tention that in Guernsey they had consolidated under the same 
conditions. 
Mr. Rurzey considered that the term ‘“‘ Hornblende-gabbro” em- 
ployed by the author was a very useful petrographical name. He 
did not think the difference of colour in some of the rocks was of 
much importance, especially as indicating bedding. He pointed out 
the interest attaching to the felstones of the Channel Islands, and 
remarked that spherulitic felstones somewhat similar to those of 
North Wales and the Lake Districts, which are of Silurian age, 
. occur in Jersey. He suggested that some of the rocks in the Channel 
Islands might possibly be of the same age. 
Mr. Topiny was inclined to regard the parallel structure in the 
eneissic rocks as bedding, and not foliation ; and the thickness of the 
strata is enormous. The rock sold as “granite” in Guernsey is 
really a syenite. There is no direct evidence that the beds are Ar- 
cheean ; but if such be their age, they may probably be correlated 
with the oldest rocks of Malvern. 
Mr. Tratt agreed with the author that parallel structure might 
be developed in igneous rocks by mechanical pressure. Diorite 
dykes in the Ardennes might be seen passing into amphibolite schists 
at their margins. Dr. Lehmann, in his recent work, called attention 
to the production not only of foliation, but also of structures simu- 
lative of bedding by the action of mechanical forces. ‘The speaker 
did not think that a persistent dip for a considerable distance in 
regions of crystalline schist could be taken as indicating a regular 
succession of enormous thickness. 
Mr. Marr asked if some of the igneous ack might not be con- 
temporaneous lava-flows. He remarked on the frequency.of the 
Q.J.G.8. No. 159. 26 
