404 F. Chapman — Constituents of Sands and Loams, 



IV. — On the Cokstituents of the Sands and Loams of the 

 Plateau Gkavel ooourring in the Pit Sections neak Ash, 

 Sevenoaks. 



By Frederick Chapman, A.L.S., F.R.M.S. 



I AM indebted to the Eev, Asliington Bullen, B.A. (London), 

 F.G.S., for eight samples of sands and loams from the Plateau 

 Gravel of Kent, which he has placed in my hands for examination 

 with the microscope. They were carefully collected by Mr. B. 

 Harrison, of Ightham ; and for convenience they are here lettered 

 A-H. 



The sections of these and other pits, made under a grant from 

 the British Association in 1895, are published in the Keport of the 

 British Association for that year. 



A. — A greyish or mottled clay, at 3 ft. 6 in. The proportion of 

 argillaceous material washed from this sample was 73 per cent., 

 leaving a residuum of 27 per cent, of fine and coarse sand. The 

 sandy residue consists of very fine angular quartz and pale 

 glauconitic fragments. There is also a large proportion of accreted 

 sand-grains, some of which simulate rhizopodal tests, if they are 

 not actually such, and resemble genera which affect sandy and 

 shallow marine areas. 



B.— A pebbly loam, from Pit No. 2, at 3 ft. 6 in. (''Ash, 1896 "). 

 A large proportion of this material consists of well-rounded pebbles 

 of flint, with an occasional subangular fragment. The sandy residue 

 after washing is seen to be composed of angular chips of flint and 

 quartz, with some ferruginous matter. 



C. — A grey sandy loam from Pit No. 1, at 5 feet. This material 

 is excessively fine. After the finest sand and clay was removed 

 by washing, the residuum amounted to 45 per cent. A part of 

 the washings was treated for heavy minerals, of which there is 

 a noticeable quantity. The average size of these mineral particles 

 is about -05 mm. in diameter. They consist of (1) Hornblende, a few 

 fragments, some with a decided blae tint suggestive of Eiebeckite ; 

 (2) Chlorite, several flakes ; (3) Tourmaline, numerous and in very 

 perfect crystals grey to greenish-brown ; (4) Kyanite, a few flakes ; 

 (5) Glauconite, numerous rounded granules ; (6) Zircon, exceedingly 

 common, some well-formed crystals with prism of 1st order and 

 pyramids of 2nd order ; also badly developed crystals with 

 rounded angles, good examples of zoning, cavities, and inclusions ; 

 (7) Butile, many examples, including both short and long prisms, 

 of a fine red-brown colour. The above-mentioned minerals are 

 much smaller than any others I have met with, either in the Bagshot 

 Sands or the Lower Greensands, but in many respects are like those 

 from the first-named deposits. The quartz gi'ains are very minute 

 and perfectly angular. There are also a few cherty and accreted 

 fragments present. 



D. — A pebbly loam, from Pit No. 2, at 8 feet. Somewhat similar 

 to the preceding ; with a difference in the character of the pebbles, 

 which, although rounded, are split apparently by frost action. The 



