some Cambridgeshire Sands and Gravels. 133 
The Collection and Preparation of the Material. 
The specimens on which the present paper is founded were 
collected from deposits of several different ages, as follows”: 
Surface Deposits. 
The Gravels of the Present River System. 
The Gravels of the Ancient River System. 
The Plateau Gravels. 
Most of the samples were collected by myself, but for some 
‘specimens of blown sands and other surface deposits from the 
‘Breckland I am indebted to Dr Marr. Whenever possible a 
fairly large quantity of the sand was collected from different 
‘points in the same bed so as to obtain a really representative 
sample. After drying, the material was passed through a sieve, 
to remove large stones, and the finer portion reserved for chemical 
and mineralogical investigation. 
The samples were first washed by shaking with water to 
remove the fine muddy material; after several repetitions of this 
‘process the sand was well boiled with water, and then dried. 
In this state it was then usually ready for éxamination with a 
pocket-lens. Very commonly, however, many of the grains were 
still covered with a pellicle of calcium carbonate or iron oxide, 
and further treatment was required to render the constituents 
visible. 
Methods of Investigation. 
In order to get rid of the calcium carbonate, most of which 
was in the form of minute particles of Chalk, the samples were 
then treated with dilute hydrochloric acid. When the effervescence 
had subsided the washing and drying were repeated and notes 
were then made on the general appearance of the samples. 
If the sand appeared to be highly ferruginous, it was then 
boiled for some time with fairly strong hydrochloric acid. This 
removed the iron oxides almost completely, and after again 
boiling with water, thorough washing and drying, the sand was 
ready for detailed examination. No doubt this treatment would 
also remove certain unstable minerals, if present, but from a 
comparison of samples, some of which had been treated with 
strong acid, and others not, it appears that the loss was not 
serious. Most of the important minerals which are likely to occur 
in sands are not affected by this treatment, and it is obvious that 
* Penning and Jukes-Brown, ‘The Geology of the Neighbourhood of Cam- 
bridge’ (Expl. quarter-sheet 51 S.W.), Mem. Geol. Surv. 1881, pp. 82—109. Marr 
and Shipley, ‘The Natural History of Cambridgeshire,’ Brit. Ass. Handbook, 1904, 
pp. 42—50. Rastall, ‘The Geology of Cambridgeshire, Bedfordshire and West 
Norfolk,’ Geol. Ass. Jubilee volume, 1909, pp. 173—177. 
