Vol. 6 8. J MINEKAL COMPOSITION OP THE AECTIG BED. 243 



Appendix YI. — The Mineral Composition of tlie Arctic Bed at 

 Pondee's End. By George MacDonald Davies, F.Gt.S. 



I. Introductory. 



During the visit of the Geologists' Association, on March 11th, 

 1911, to the Great Eastern liailway Company's ballast-pit at 

 Bonder's End,^ I collected a sample of the late Pleistocene marsh- 

 deposit known as the Arctic Bed, with a view to washing ont the 

 fossils. A casual examination of the sandy residue left after washing 

 suggested that a more systematic study of the mineral composition 

 of the deposit would be of some interest. The need of more 

 material was met by Mr. S. H. Warren, who very kindly supplied 

 six samples, weighing 16 pounds when received, selected from 

 different parts of the bed. These six samples form the basis of 

 the present note. 



II. Method of Examination. 



The method of examination employed was as follows : — The 

 air-dried sample was broken into small pieces, and desiccated in a 

 steam-oven until the weight became constant. It was then washed, 

 the muddy water being poured through a 60-mesh wire sieve, 

 which collected most of the vegetable matter. A final separation 

 of the clayey particles from the sand was obtained by well boiling 

 the material, after which the sandy residue Avas dried and 

 weighed. Eor quantitative purposes, a 50-gramme sample of the 

 sand was treated with bromoform of specific gravity 2*85, and 

 the portion that sank was weighed. The rest of the sand was 

 panned down, and the concentration completed by bromoform. As 

 a precaution against contamination, no sieves were used until the 

 lieavy minerals had been separated from the sand. The portion 

 heavier than bromoform included, besides detrital minerals, varying 

 proportions of earthy pyrrhotite, pyrites, and iron-oxide. The 

 first was separated by an ordinary horseshoe-magnet ; the iron- 

 oxide was removed by hot dilute hydrochloric acid, and the pyrites 

 by weak nitric acid — a portion of the concentrate being first 

 examined for other minerals soluble in these acids. The residue, 

 after further treatment with bromoform, may be regarded as the 

 total detrital heavy minerals present in the material, the sulphides 

 and oxides of iron being of chemical origin. This residue was 

 separated into three portions by the electro-magnet, and examined 

 under the microscope in the usual way. 



^ Proc. Geol. Assoc, vol. xxii (1911) pp. 166-71. 



