some Cambridgeshire Sands and Gravels. 141 
GENERAL CONCLUSIONS. 
The most abundant constituent in all the sands here examined 
is, as might be expected, quartz. This is normally perfectly clear 
and colourless, but sometimes shows a reddish tinge. Next in 
abundance is flint, in white opaque grains, often well rounded. 
In many samples Chalk is abundant, while prisms of Inoceramus 
and Echinoid spines derived from the Chalk are often common. 
Glauconite is generally present, although not conspicuous till the 
sands are cleaned, since the grains of this mineral are frequently 
covered by a skin of iron oxide, which must be removed by acid 
before they become readily visible. The heavy residues, of a 
density higher than 295, include a large proportion of opaque 
grains of magnetite and other oxides of iron. Among the trans- 
parent constituents of the heavy residues the following are generally 
present: garnet, tourmaline, kyanite, staurolite, hornblende, augite, 
hypersthene, epidote, zoisite, zircon, rutile. Of these the most 
abundant is, in most cases, garnet, which occurs in angular, sub- 
angular and rounded fragments often of considerable size; tour- 
maline varies much in colour, and blue varieties are common ; 
other colours noted are brown, pink and green. Staurolite is 
common, always in angular fragments, while the numerous 
crystals of kyanite are notably more angular in the older gravels. 
Hornblende is locally very abundant and includes the blue variety 
(arfvedsonite) which is so characteristic of Norwegian soda-rocks. 
Zircon is much less common than in most sands, e.g. the Bagshot 
Sands described by Dick. 
The minerals of these sands may be divided into two groups, 
as follows: 
A. Glauconite, tourmaline, kyanite and staurolite: these are 
almost certainly derived from the Neocomian. As is well known, 
staurolite nearly always remains angular, but the tourmaline and 
kyanite are somewhat more rounded than in that formation. The 
tourmaline especially occurs in extraordinarily well-rounded forms. 
The blue variety, which is common, is almost certainly derived, 
vid the Lower Greensand, from the ancient Armorican land to 
the south-west. Kyanite is a very common and characteristic 
‘mineral both in the Carstone and in the Sandringham Sands, and 
staurolite is also present in both of these. The abundance of 
glauconite in the Neocomian hardly needs mention. 
B. Garnet, hornblende, augite, hypersthene, epidote: these 
minerals are almost unknown in the Neocomian, and have 
certainly been derived at first hand from the disintegration of 
far-travelled rocks of Scotch and Scandinavian origin during the 
