t 



WALTOJf COMMON EXPOSING LONDON CLA.T ETC. 161 



and I will now proceed to make a few observations on the Bagshot 

 Sands of this place, selecting No. 1 as the type, because the con- 

 stituent grains are comparatively large, and because, where it is 

 thick and current-bedded, the grains are remarkably free from 

 ochreous or other investment. 



The sample now under description was taken from the very 

 thickest part of the bed and towards the middle of it : it is a light- 

 grey sand with black specks, passing laterally into bright-yellow 

 sand. The following are the chief constituents in order of abun- 

 dance : — 



(1) Vitreous quartz, mostly angular: size of grains ranging from 

 about 0'9-0'27 millim., average perhaps 0*4 millim. This forms 

 the bulk of the sand. 



(2) Opaque and coloured quartz, partly, perhaps, chalcedonic: 

 grains often rounder and slightly larger than in the other variet)'. 



(3) Angular, subtransluceut fragments, black in reflected light, 

 believed to be chips of flint or chert. Also angular fragments of a 

 dull black mineral, probably the "lydite" of authors. 



(4) Green renuline granules, some of which must evidently have 

 been casts of organisms, probably Foraminifera. These granules 

 are smaller, on an average, than the quartz grains, and are fre- 

 quently fractured, appearing as fragments. They are not sufficiently 

 numerous to materially affect the colour of the sand. Doubtless 

 this is the so-called " glauconitc," which, in the present case, I take 

 to be mainly a hydrous ferric silicate, with variable proportions of 

 alumina and small quantities of protoxide bases. 



(5) Granules of iron-oxide here and there ; magnetite extremely 

 scarce. 



Siqyjplementari/ Note as to Nos. 1 and 2 Bagshots. 



K'o. 1. A fresh sample of this clean bright sand confirmed the 

 features already indicated. Many fine examples of glauconite in 

 renuline granules, some after Glohigerina. The average size of the 

 granule in this sample was estimated at J millim. 



Noted an oval grain of quartz, 2| miilim. in length. The dark 

 flakes are evidently some chalcedonic form of silica ; but how is it 

 that they are not bleached like the flint chips in the sands of the 

 gravels? A single small fragment may be a bleached flint chip. 



No. 2. The sandy beds of No. 2 contain a considerable amount of 

 iron mineral. The red sands of this series and associated clays 

 contain quartz pebbles up to 4 and o millim. in diameter. 



About the junction of Nos. 1 and 2 are numerous woody frag- 

 ments bored by Teredo, and afterwards partly pyritized. Very often 

 hardly anything is seen but the form of the tube associated with 

 brown oxide of iron. 



The next bed which has to be considered is No. 2, or the Blue 

 Bagshots : this is mainly argillaceous, but with seams of sand in- 

 cluded, which are often rather coarse and very ferruginous. As 

 before remarked, the lithology of this bed varies so much within 

 short distances that a detailed description would be interminable. 



