354 ME. H. B. MILIS'ER ON THE [vol. Ixxviii, 



The coarse material was first carefully examined with a lens, and 

 subsequently with the microscope, in the latter case by placing 

 some of the grains on a black card and viewing them by reflected 

 light. The medium and fine material were both washed with 

 water, treated with a dilute solution of hydrochloric acid so as to 

 remove any ferruginous coating of the grains, and in the case of the 

 fine grade, boiled previously with a 1 per cent, solution of sodium 

 carbonate to deflocculate silty and clayey matter. The clean sand 

 was then dried, and about a third taken for treatment with * heavy' 

 liquids. (A jDreliminary trial in all cases showed that these Plio- 

 cene deposits yielded abundant residue, and consequently there was 

 no necessity for utilizing the whole of the cleaned sample, except 

 for quantitative determination.) 



For the * heavy ' mineral concentration bromoform of specific 

 gravity 2*821 and, in special circumstances, cadmium borotungstate 

 of specific gravity 3 '28 were used. The residues thus obtained 

 were separated with an electromagnet into magnetic and non- 

 magnetic crops ; these were then mounted in Canada balsam for 

 microscopical examination, and a slide was made in each case of 

 the * light ' material of the sample, s.g. <2'82. The total amount 

 of ' heavy ' mineral concentrate obtained in all cases was mounted, 

 to ensure inclusion of the rarest mineral species present in the 

 sediment. 



In many instances the samples were examined quantitatively, 

 and the percentages of light material, ferruginous cement, silt and 

 clayey matter, and ' heavy ' residue determined. Such results are 

 included below in the section dealing with the petrography of the 

 various deposits. 



IV. LiTHOLoaicAL Chaeactee of the Deposits. 



(a) St. Agnes. 



The deposits here consist of a well-marked series of yellow, 

 white, and brownish-red sands overlain by grey and mottled clays. 

 The principal section exposed at Higher Bal, west-north-west of 

 St. Agnes Church, shows abont 6 feet of sand, yellow at the base, 

 and passing up into an almost pure white sand, which gives place 

 to a brownish-red facies immediately beneath the clay. The 

 transition from the sand to the clay is actually not so sharp as at 

 first sight appears, and an intermediate arenaceous clay separates 

 the sands below from the true clays above. The sanely clay and 

 overlying grey and mottled clays in this section vary from 7 to 

 8 feet in thickness, although this facies tends to thicken south- 

 westward ; as in the Beacon Cottage pit no sand is exposed, and 

 8 to 10 feet of clay occur. The sands themselves occasionally 



^ Since the War, tlie bromoform put on the market has varied considerably 

 in purity, and the specific gravity has fluctuated accordingly ; in some cases 

 it was possible to raise the gravity to 2*9 by repeated distillation, but not 

 without great trouble and a certain amount of loss. 



