188 Reports and Proceedings—Geological Society of London. 
associated gold) ascended along the fractures due to the intrusion 
ot the dyke, and found an easy course along the small conglomerate 
bed, where they replaced some of the quartz pebbles with pyrites, 
being kept up by a band of shale underneath the conglomerate. 
IV.—March 13th, 1907.—Aubrey Strahan, Sc.D., F.R.S., Vice- 
President, in the Chair. 
The following communications were read :— 
1.'¢¢A Silurian Inlier in the Eastern Mendips.” By Prof. Sidney 
Hugh Reynolds, M.A., F.G.S. 
An account of the rocks with which the paper mainly deals was 
brought before the Society on February 7th, 1906 (see Abstract of 
Proc., Grot. Mac., 1906, p. 142); but, owing to the discovery just 
before the meeting of Silurian fossils in material thrown out by moles 
and rabbits, the paper was withdrawn and further work, including the 
digging of a series of seven trenches, was carried out. This proved 
that the fragmental igneous rock is of two types:—(1) Normal fine- 
grained tuff, from which in three localities over thirty species of 
Silurian (probably Llandovery) fossils were obtained and have been 
identified by Mr. F. R. Cowper Reed: the tuffs are seen at Sunnyhill 
to underlie the trap. (2) A remarkable coarse ashy conglomerate, 
the nature and relation of which to the other rocks are both 
obscure. The following four possibilities with regard to the nature 
of this rock are discussed in some detail:—(a) That it may be the 
basement conglomerate of the Old Red Sandstone; (3) that it may 
be an aqueous deposit of the same general age, and belonging to the 
same igneous series as the associated trap and normal tuff; (¢) that 
it may be an old river-gravel, deposited during a terrestrial period 
subsequent to the fossiliferous Silurian and prior to the Old Red 
of the district; and (d) that it may represent the necks of the 
volcanoes from which the trap and the normal tuff were ejected. 
The author is of opinion that the fourth of these possibilities agrees 
best with the observed facts. The paper concludes with a comparison 
between the Mendip Silurian rocks and those of Gower and Tortworth, 
in both of which localities it appears that the upper beds of the 
Silurian System are unrepresented. 
2. ‘On Changes of Physical Constants which take place in certain 
Minerals and Igneous Rocks on the Passage from the Crystalline to 
the Glassy State; with a short Note on Eutectic Mixtures.” By 
James Archibald Douglas, B.A., F.G.S. 
After giving an account of previous experiments in the direction 
of determining the physical changes accompanying the fusion of 
rocks and minerals, and their re-solidification into a glassy condition 
—experiments which are in many cases open to sources of considerable 
error—the author describes the electrical apparatus employed by 
himself. Powdered rock of known specific gravity is fused as often 
as required in a loop of platinum-ribbon. The fused product is 
powdered, examined with the microscope, and then placed in 
a diffusion-column, by the use of which errors due to the few small 
