334 Reports & Proceedings—Geologists’ Association, London. 
a large, tumid, laterally compressed cone, with one well-separated 
posterior cusp. 
IV.—Geotoetsts’ Association, Lonpon. 
June 2, 1916.—George Barrow, Esq., F.G.S., President, in the Chair. 
The following paper was read: ‘‘The Petrology of the North 
Sea Drift and Suffolk Brick-earth.” By Perey G. H. Boswell, D.Sc., 
F.G.8., A.R.C.S. 
1. The varied facies of the North Sea Drift and Suffolk Brick-earths. 
Mechanical analyses; graphical representation of results; economic 
values; comparison with other British deposits. 
2. Petrography. Detrital residues and comparisons with residues 
from other glacial beds. 
The paper was a sequel to that published by the Geological 
Association in 1913, dealing with the field evidence which served 
to distinguish the North Sea Drift (Lower Glacial) from the Brick- 
earth of Suffolk (Upper Glacial). 
The three facies of the North Sea Drift, (a) the Cromer Till, etc., 
of the coast sections, (b) the Marly Drift of the Western area, and 
(c)the inland Norwich Brick-earth, were briefly considered. Mechanical 
analyses were given of the deposits, and expressed graphically by 
means of curves. The Lower and Upper Glacial deposits were shown 
to conform to very different types, pointing to different modes of 
genesis. They could easily be distinguished from one another by 
grade composition. 
Although small variations in mineral composition occurred, the 
Upper and Lower Glacial Brick-earths did not each possess a distinctive 
and differing mineral assemblage. As would be expected from the 
varied sources of their constituent materials, the glacial deposits 
generally yielded an exceedingly rich and beautiful assemblage 
consisting of over forty mineral species, many of which were derived 
directly from the breaking up of fresh igneous rocks. The most 
abundant detrital minerals included garnets, epidotes, hornblendes, 
‘and pyroxenes (soda-bearing varieties included), hypersthene, micas, 
staurolite, kyanite, andalusite, apatite, and others. 
A lecture was also delivered (illustrated by lantern views) entitled 
‘Notes on Erosion Phenomena in Egypt ’’, by Miss Mary S. Johnston, 
F.R.G.S. 
Amongst other phenomena of erosion the lecture illustrated the 
decomposed igneous rocks at the Second Cataract, and the pot-holes 
and shade-weathering in the granite of the First Cataract. The 
variation in the constituents of the Nubian Sandstone, the rivers 
of blown sand on the west of the Nile, and the famous quarries 
of Gebel Silsileh were described. Reference was made to interesting 
geological features of the Theban mountains, notably the Eocene 
chert concretions, and the dry river-valleys and gravels. The 
significance of certain sites from which numerous worked flints have 
been collected were also considered and illustrated by views and 
specimens. The action of the sun, wind, and water upon the 
Mokattam limestones was referred to in connexion with the formation 
of Wadi Hof and the production of the etched surface of the Sphinx. 
