some Cambridgeshire Sands and Gravels. 137 
recorded, including scratched blocks of Carboniferous limestone, 
Millstone Grit, basalt, pink granite and rhomb-porphyry™*. 
The sand is fairly clean, of a light brown colour, and 
effervescing very freely with acid. In this case a double 
separation was found necessary, and the light residue from the 
second separation was found to consist largely of glauconite, 
which had been coated with iron oxide. 
Among the heavy minerals of this specimen, the following 
were identified: pink garnet, tourmaline, both brown and blue, 
staurolite, kyanite, epidote, hornblende, augite and hypersthene, 
together with black grains which are presumably magnetite. 
Zircon is very rare. The most notable features are the extreme 
angularity of most of the garnets, and the comparatively large 
size of the heavy mineral grains. 
(c) Furze Hill, Hildersham, 200 ft. above O.D. 
This specimen was obtained from the actual bed in which a 
Palzolithic implement was found in situ by Dr Marrf. It is a 
yellowish brown rather coarse sand with many small flints. After 
cleaning in the usual way the sample was found to consist chiefly 
of grains of clean white quartz, many of which are notably rounded. 
Coloured minerals are not abundant, consisting chiefly of grains of 
iron oxide. After separating in bromoform the heavy residue was 
examined microscopically, and was found to contain rounded grains 
of iron oxide together with brown and blue tourmaline; staurolite, 
zircon, rutile, garnet, and a very little kyanite. Most of the heavy 
grains are very much rounded, and they show much variation in 
size. 
This sand is very unlike the specimen collected at about the 
same level on the Gog-Magog Golf-Links, and has evidently been 
laid down in rapidly moving water, with much more rolling of 
the grains. This fact helps to confirm the idea put forward by 
Dr Marr+, that these gravels and sands belong to the ancient 
river-system rather than to the plateau gravels. 
III. Gravels of the River Cam. 
Highest or Barnwell Terrace. 
(a) Gravel Pit close to L. and N. W. Railway bridge between 
Trumpington and Shelford, 60 ft. above O.D. 
This pit shows chiefly a moderately fine flint gravel of the 
usual type, with occasional seams of sand. From the most 
* Rastall and Romanes, ‘The Boulders of the Cambridge Drift,’ Quart. Jour. 
Geol. Soc. Vol. uxv. 1909, p. 254. 
+ Marr, ‘On a Paleolithic Implement found in situ in the Cambridgeshire 
Gravels,’ Geol. Mag. 1909, pp. 534—537. 
