PLEISTOCENE GEOLOGY OF THE THAMES VALLEY. 343 



(I.) WESTERN PORTION. 



(a.) Tunnel Cement Works. A good section of the Middle 

 Terrace Drift as represented in the western portion of the district 

 is exposed in the quarry of the Tunnel Cement Works. This 

 section exhibited, in 1900, the drift piled up against the old chalk 

 cliff which formed the bank of the Pleistocene Thames at this 

 stage in its development. 



The beds shown in the section are : — 



1. Surface soil and " wash gravel," about 4 feet. 



2. Stiff brown loam, about 4 feet. 



3. Finely laminated sand, with occasional seamsof argillaceous material. 

 Two well-marked bands of pebbles were exposed, occupying respectively the 

 top and bottom surfaces of the middle third of this series. The lower pebble 

 band consisted chiefly of well rounded flints, but in the upper bed in addition 

 to these were many small fragments of chalk, mostly well rounded, and a few- 

 unworn chalk flints. Towards the base of the series large chalk pebbles 

 became more abundant, until at last near the junction with the chalk clift 

 they formed two-thirds of the total detritus. This portion of the series, 

 however, was easily distinguished from the underlying chalk-rubble by its 

 perfect stratification and the well rounded character of the included fragments 

 of chalk. As the beds approached the south, i.e., as they receded from the 

 old bank so the pebbles of chalk became fewer, until not one could be found 

 in the basal portion. In places the beds are somewhat indurated, this condi- 

 tion probably arising from contraction during drying. The arenaceous con- 

 stituents appear to have been wholly derived from the Thanet Sands of the 

 neighbourhood. The total thickness of the beds included in this division is 

 from 16 to 20 feet. 



4. Chalk rubble, angular and unstratified, about 6 feet. 



5. Chalk. 



Mr. W. J. L. Abbott, F.G.S., described this section in 1890 

 (60) and recorded several species of the usual larger Pleistocene 

 Mammalia and also seven species of Mollusca. The species are 

 all included in our general list from Grays Thurrock. 



(b.) Pit -west of Milwood Lane. Proceeding eastwards 

 along the London Road, the next exposure of the brickearths is 

 that seen in the tramway cutting of the quarry belonging to 

 Messrs. Gibbs. The section was briefly described by Mr. W. 

 Whitaker, F.R.S., in 1889, in the " Geology of London," (59), 

 and he figures it as it was in 1872. Since that time it has been 

 deepened, but no further detail of much importance is to be 

 seen. The section resembles that seen in the Tunnel Pit in 

 showing the drift piled against an old chalk cliff. The details 



