i 
A 
Reports and Proceedings—Geological Society of London. 379 
‘« The scientific logical classification of igneous rocks must apparently be based on 
the quantitative development of fundamental characters, and the divisions of the 
scheme must have sharp artificial boundaries, since none exist in Nature. 
‘* Chemical composition is the fundamental character of igneous rocks, but it may 
be advantageously expressed for classificatory purposes in terms of simple compounds, 
which represent either rock-making minerals or molecules entering into isomorphous 
mixtures in known minerals. It is probable that the magmatic solution consists 
of such molecules, and that the norm of the ‘ Quantitative System’ is a fairly 
representative set of these compounds. 
‘¢ The actual mineral and textural characters of igneous rocks are variable qualifiers 
of each chemical unit, and should be applied as such to terms indicating magmatic 
character.”’ 
2. ‘*The Denudation of the Western End of the Weald.” By 
lenny bury, MA. F.1L.S., F.G.S. 
There are two main theories of Wealden denudation—(1) attributing 
the removal of most of the Chalk to marine planation ; and (2) denying 
planation and relying solely on subaérial denudation. Professor W. M. 
Dayis’s suggestion of a subaérial peneplain forms a sort of connecting 
link between the two. 
The evidence in favour of planation which Ramsay and Topley 
brought forward is inconclusive, and might plausibly, if it stood alone, 
be attributed to pre-Eocene causes. On the other hand, Prestwich’s 
arguments against planation are equally weak, while the Chalk plateau 
to which he draws attention strongly supports Ramsay’s views. The 
distribution of chert is fatal to Professor Davis’s hypothesis, and very 
difficult to account for, except on the marine theory. 
In the case of the River Blackwater it can be proved that, long 
after the Hythe Beds of Hindhead were uncovered, the river-system 
remained extremely immature, and this affords very strong grounds 
for the acceptance of the marine hypothesis: 
The evidence of the other western rivers is less conclusive, though 
the Wey and the Mole both provide minor arguments pointing in the 
same direction. ‘The anomalous position of the Arun, at the foot of 
the northern escarpment of the Lower Greensand on either side of the 
Wey, is almost certainly due to comparatively recent captures from 
the latter river, and affords no ground for assuming a river-system of 
great age matured on a Miocene peninsula. 
There is no proof that any of the existing connexions between rivers 
and longitudinal folds are of a primitive character, and, on the other 
hand, there are many alleged examples of transverse disturbances 
having served as guides to consequent rivers. This again, on the 
whole, supports the marine hypothesis, especially if, as there are 
reasons for believing, the longitudinal folds are older than the 
transverse. 
3. ‘An Earthquake Model.” By John William Evans, D.Sc., 
TiLB., F.G:S. | 
This model is designed to show the successive conditions that result 
in an earthquake shock— 
(1) Slow relative movement between two extensive portions of the earth’s 
crust lasting over a long period, and causing 
(2) a state of strain im the intervening tract, leading to 
(3) fracture which relieves the strain and allows 
(4) the adjoining portions of the rock on either side to fly back by virtue of 
