Geological Society of London. 237 
in connection with the probability that the Huronian and Kewenian 
beds are of littoral origin. 
2. “The Occurrence of Colloid Silica in the Lower Chalk of 
Berkshire and Wiltshire.” By W. Hill, Esq., F.G.S., and A. J. 
Jukes-Browne, Hsq., F.G.S. 
In the Lower Chalk of Berks and Wilts are beds which contain a 
large amount of disseminated colloid silica; these are comparable in 
general structure to the Malmstones of the Upper Greensand. Dr. 
Hinde’s study of the latter led him to believe that the globular 
colloid silica which they contain was directiy derived from the 
remains of siliceous sponges, and the authors’ studies of the Chalk 
specimens have confirmed this conclusion by adding several im- 
portant pieces of evidence. 
They found that the amount of free disseminated silica increases 
in proportion to the number of spicules and calcite-casts of spicules 
which occur in the rock, and observed that the great similarity be- 
tween the siliceous chalk and the Malmstone was heightened by the 
occurrence of similar siliceous concretions in both rocks, the material 
of which might be described as siliceous chalk, indurated by a cement 
of chalcedonic silica. ‘The conditions in which the silica was found 
in the Lower Chalk were described, in examples varying from those 
containing least to those which held most silica; in the latter the 
amount of colloid silica was estimated at 12°61 per cent. by weight. 
After noticing the vast amount of silica present in rocks with a 
maximum thickness of 70-80 feet, the authors discussed the diffi- 
culty of accounting for this, and drew attention to Prof. Sollas’s 
statement that many living siliceous sponges constantly shed some 
of their spicules. 
A further question arose as to whether the formation and accu- 
mulation of globular silica went on contemporaneously with the 
deposition of the calcareous material upon the sea-floor, or whether 
the conversion of the spicules into such silica took place after the 
consolidation of the rock, and the authors gave reasons for sup- 
posing that the latter was the case, the change having occurred 
when the rock was in a sufficiently oozy condition to admit of easy 
molecular distribution. Reasons were given for supposing that the 
disseminated colloid silica had not been derived directly from the 
disintegration of spicules in which a globular structure had been 
previously developed, but that the globular silica was precipitated 
from solution whilst the beds were still permeated by sea-water. 
The precipitation of the chalcedonic silica was regarded by the 
authors as a secondary and subsequent operation. ‘They were dis- 
posed to regard all nodular concretions resembling flints and phos- 
phatic nodules as growths, which were more or less contemporaneous 
with the deposition of the materials of the enclosing rock, and in 
conclusion they offered some comments upon the problem of the 
formation of flints. 
3. “Note on the Pelvis of Ornithopsis.” By Prof. H. G. Seeley, 
F.R.S., F.G.S. 
The remains preserved in Mr. Leeds’s collection at Hyebury, and 
