Notices of Memoirs—Dr. Boswell—Glass Sands. 467 
the medium-sand grade (diameter >4 and<imm.). A high percentage 
of the fine-sand grade (diameter >and <;mm.) would be even 
more preferable, but suitable sands with a high proportion of this 
grade are not of common occurrence in this country. Coarser sand- 
grains are not desirable, and, if present, should be removed by 
sieving. Very fine sand, silt, and clay-grades are inimical, and must 
be removed by washing. 
3. The mineral composition should be as simpie as possible, 
contain only quartz, or quartz and felspar, and the heavy detrital 
minerals present should be small in quantity and simple in com- 
position. 
The treatment of sands (whether chemical, to remove iron, or 
mechanical, to ensure good grading) often involves prohibitive 
expense. It is therefore of considerable importance to look into the 
geological conditions under which desirable glass-sands occur. We 
may thus receive clues to the existence of further supplies by knowing 
the kind of deposits in which they are met, and the special conditions 
under which we may expect to find them. The important supplies 
of glass-sands occurring in Western Europe are associated with rafts 
of braunkohle in beds of Miocene age; Hohenboka sand, of the 
same age, containing carbonaceous layers; Fontainebleau sand, in 
Upper Oligocene deposits, with lignites; Inferior Oolite sands in the 
Yorkshire and Northampton districts, containing planty matter and 
roots; Berrythorpe sand (Callovian), containing carbonized woody 
material and peaty matter; Aylesbury and Leighton Buzzard sands 
(Lower Greensand) with peaty bands; Headon Hill and Bagshot. 
from Alum Bay, Wareham, and other places (Hocene, etc.), inter- 
bedded with lgnites. Numerous other examples may be adduced. 
Attention also may be drawn to the very pure sandstones of the 
Coal-measures, associated with coal-seams, and to the white sandstones 
found with the Brora coals of Scotland (Callovian). The bleaching 
‘of the reddish sands, for a foot or two in depth, upon our heaths, is 
a similar phenomenon. In each case the freedom from iron may be 
attributed to the reducing action of the planty matter, in changing 
the ferric salts to the more soluble ferrous state, when they are more 
easily removed by percolating waters. 
The beds of white sand seem always to be of limited thickness, and 
frequently to be laid down under lagoon or estuarine conditions 
favouring the development of plant life. Cementation is objectionable, 
either because of the introduction of impurities or because of the 
cost of subsequent crushing. It is desirable, therefore, that the 
deposits should be incoherent. The most widely used sands are thus 
those of comparatively late geological age. Most of them occur in 
Tertiary deposits, but some are Cretaceous in age. A _ strong 
tendency, also, exists for the simplification in mineral constitution 
(due to elimination of more easily decomposable minerals) and greater 
perfection of grading in the later geological sediments—a result of 
their constituents having passed through many geological cycles. 
[This, and the two following Notices, are Abstracts of papers read in 
Section C (Geology), British Association, Newcastle-on-Tyne, September, 1916. ] 
