some Cambridgeshire Sands and Gravels. 135 
by Pholas or some other rock-borer. The presence of these and 
of the Cretaceous rocks of Norfolk type is of special significance, 
as indicating derivation of the material from the Wash district. 
Rounded pebbles of Chalk are abundant, but they are believed 
to be of Yorkshire type and the large grey tabular flints are much 
more like those of Lincolnshire than of any more southern 
locality *. 
The bed of sand, about 5 feet thick, which is now being 
worked for use on the golf-links, is of very fine texture, marly 
and rather tenacious, of a yellow-brown colour. It differs much 
in appearance from other sands of the district. It effervesces only 
feebly with dilute acid, but very large quantities of fine mud are 
removed by boiling with water and subsequent washing. Chips 
of white flint are common, but the most notable constituent seen 
on macroscopic examination is mica, both white and brown, together 
with glauconite. As will appear later, mica is almost completely 
absent from the other sands investigated. 
From a first separation, without preliminary treatment with 
acid, the heavy residue was very large, and mostly of a brown 
colour, owing to the presence of a coating of limonite. In this 
state identification of the grains was impossible, and the residue 
had to be digested with acid and again separated. 
On examining a microscope-slide of the ultimate residue the 
first feature to be noticed is the small average size of the grains, 
which are much less than those of the other gravels of the 
Cambridge district, and can only be compared in this respect 
with the blown sands from the neighbourhood of Brandon, to be 
afterwards described. 
The following is a list of the principal minerals identified : 
hornblende, augite, garnet, epidote, zircon, tourmaline, rutile, 
magnetite and other iron ores, and abundant flakes of muscovite. 
Kyanite and staurolite are notably rare. Hornblende is extra- 
ordinarily abundant, both the common green variety and greenish 
blue arfvedsonite. Tourmaline is also abundant and shows many 
shades of colour, brown, pink, blue and green: the grains are as 
usual very well rounded. In comparison with other local sands, 
pyroxenes, epidote and zoisite are common. 
The most striking features of this sand are the abundance 
of hornblende and muscovite, and the strange shapes of many 
of the grains, which can best be described as sharply angular 
chips. It is evident that in the case of most of the constituents 
there has been little rolling, either by water or wind action; only 
the grains derived from some older formation, such as tourmaline 
and kyanite, are conspicuously rounded. The significance of the 
* Rastall and Romanes, ‘The Boulders of the Cambridge Drift,’ Quart. Jour. 
Geol. Soc. Vol. txv. 1909, p, 254. 
