280 Reports and Proceedings— 
“Tn a section of the London Clay exposed during building opera-' 
tions about 200 yards south of Gipsy Hill Station, I noticed scattered 
through the clay some small masses of free angular siliceous sand. 
These were of irregular shape, 1 to 2 inches in diameter, and the clay 
around them was perfectly homogeneous, and free from siliceous 
grains, no difference being noticeable in its texture or colour. After- 
wards I observed the same bodies in clay thrown out from an 
excavation for drainage purposes, nearly a quarter of a mile away. 
The masses were distributed in great numbers horizontally through 
the clay, occupying a thickness of about eighteen inches; but not 
deposited in layers, and without any special indication of stratifica- 
tion within that part of the bed. The London Clay was deposited 
in the nearly still-water of a large estuary ; and the question arises, 
how did these masses of sand come there? It is evident that they 
could not have been carried by the water which brought the fine sedi- 
ment forming the clay of the bed; and as it is in well-defined masses, 
it must have. been held together in some way. Considering the high 
temperature which the fossils of the London Clay indicate, one cannot 
consider ice as the cause of holding the sand together. If the cement, 
then, was mineral, it must have been re-dissolved and removed at 
a later stage, so as to leave the sand free. If it had been iron, we 
might expect that it would have specially coloured the surrounding 
clay, but of this there is no trace. It appears to me that carbonate 
of lime was probably the material which cemented the masses; but 
J have not been able to find a satisfactory explanation as to the 
means of its carriage and causes of its deposition. The cause of 
deposition may have been extremely local, as there is no evidence 
of the deposit being continuous between the two points observed ” 
PD). 
We cannot close this brief notice without wishing the members of 
the Dulwich College Science Society the success they merit, and trust 
they will persevere in the pursuit of science in all its branches. 
ee Omens AND, evo CSC 2D Ee 
—— 
GEOLOGICAL Society oF LonpDon. 
I.—April 11, 1883.—J. W. Hulke, Esq., F.R.S., President, in the 
Chair.—The following communication was read :— 
‘“On the Supposed Pre-Cambrian Rocks of St. David’s.” Part II. 
By Archibald Geikie, Esq., F.R.S., F.G.S. 
In this second part of his paper the author gave the results of the 
survey which he had made of the district with Messrs. Peach and 
Topley, and of his study of a series of more than 100 thin slices of the 
rocks collected at St. David’s. He found that he could corroborate 
generally the descriptions of previous writers on the microscopic 
structure of the rocks, and that investigation with the microscope 
amply confirmed the deductions he had drawn from observations in the 
field. 
1. Order of Succession of the Rocks.—The following rock-groups in 
