26 PROF. T. G. BONNEY ON THE GEOLOGY 
EXPLANATION OF PLATE I. 
Structure imitative of foliation produced by pressure on a stratified rock 
without important mineral change. 
The mass of rock figured is about four feet high. The cleayage-structure is 
vertical ; the beds (of alternating dark mud and paler silt) are bent into rather 
irregular curves pointing downwards, and are separated as described in the 
text. The paler parts of the figure represent the ‘streaks’ and ‘eyes’ of the 
silty rock, made sometimes more distinct by aggregations of quartz. 
Discussion. 
Mr. J. Srarxre Garpwer stated that the EKocenes of freshwater 
origin of the south of England were formed from granitic materials, 
and not from flints, the Chalk not being then upheaved ; and these 
facts seemed to lend support to the author’s conclusions. 
Rev. G. F. Wuipporne said that somewhat similar beds at Hope 
Nose contained the fossils of the Middle Devonian. He asked if 
the rocks dredged in mid channel by Mr. Hunt at all resembled 
those of the coast. 
Rey. HK. Hixu asked if the gneiss mentioned by Sir H. de la Beche 
resembled any rock of the Lizard. He agreed with the author that 
the lenticular structure described is such as would be produced by 
the oblique crushing of a mass. He stated that in the Channel 
islands none but the most highly metamorphic rocks occur. 
Prof. T. McK. Hueuuzs pointed out the close resemblance of the 
enarled beds of Prof. Bonney’s post-Archean slates to the gnarled 
beds of Amlwch, which he (Professor Hughes) had described as not 
truly metamorphic, but only mechanically altered rock. He thought 
that the lowest Archean of Britain and France was sometimes 
granitoid rock, sometimes schist, and that they alternated and 
passed into one another, so that no general order could be established 
between granitoid rock and the lowest schists. In Brittany he had 
observed such alternations, especially in the remarkable sections 
along the river Rance, near Dinan. 
He called attention to the thickening of sediment from north to 
south, 2. ¢. towards the English Channel, in the two groups which 
next succeeded the Archean, viz. the Lower Cambrian and the 
Devono-Carboniferous, and thought that these facts must be taken 
into consideration when speculating upon the probability of the 
pressure than to mineral composition or geological age. Such rocks as the 
phyllites of the Ardennes and of the Alps, not to name others, have, as a rule, 
little claim to be classed with the true schists—the foliated rocks. They have, 
indeed, taken a step in that direction, but it is only a small one, and their 
alteration should be classed with the phenomena of mechanical rather than 
of chemical metamorphism, although the latter has operated to a slight extent. 
Still, though pressure is an important agent, it is not, as these words imply, the 
ouly agent ; and when marked regional metamorphosis prevails, when we are 
considering great masses of truly foliated rock (gneisses and schists), we seem 
to require something more. Are we justified in asserting that the other neces- 
sary agencies operated more freely in Archzan times than they have subse- 
quently done ? 
