PRESTWICH WOOLWICH AND READING SERIES, 127 



feature of this series. At Newbury the proportion of sands de- 

 creases, but these beds again become more important in proceeding 

 from Newbury towards Marlborough. Now it is precisely in these 

 directions that the blocks of grey weather sandstone set in and attain 

 their greatest development*. On the hills above Goring sandstone 

 blocks are not uncommon ; and I have here recently found the mottled 

 clays, associated with a thick bed of white quartzose sand, ranging 

 close to the edge of the chalk escarpment from Woodcot Common to 

 near Combe End Farm. Crossing the gorge of the Thames the same 

 beds are found capping the hills at Bassildon, and a trace of them 

 apparently exists near Aldworth. In fact, throughout the chalk 

 district of Wilts, Berks, Oxfordshire, Bucks, Herts, and Kent, the 

 tertiary outliers are far more common than has been supposed. They 

 distinctly show the former spread of the Lower Tertiaries, the Wool- 

 wich and Reading series especially, over the whole area, up even to 

 the very edge of the chalk escarpment. 



In the direction of High Wycombe and Nettlebed the sand beds 

 are again in excess. On the chalk hills above Bradenham, three 

 miles northward of the former town, sandstone blocks are very nu- 

 merous, and, although enveloped in a ferruginous clay-drift, they 

 are, I believe, nevertheless nearly in sitw^-. Around Hedgerley and 

 Uxbridge, where mottled clays prevail, few sandstone blocks occur. 

 In the neighbourhood of Hatfield, Hertford, and Ware, the sands 

 of the Reading series, perfectly white and sihceous, are often, if I 

 may use the expression, glutted with flint-pebbles ; it is over this 

 area more particularly that the Hertfordshire pudding-stones are so 

 abundant. 



Beneath and also to the south and south-east of London, a very 

 hard, light-coloured, fine-grained, calcareo-argillaceous rock, usually 

 without fossils, is often present in the lower part of the Woolwich 

 beds just under the shelly clays. This bed, however, rarely exceeds 

 the limits of the fluviatile and estuarine clays, and forms therefore a 

 mere local feature. At Gravesend we find in nearly the same position 

 a thin tabular layer of hard siliceous sandstone. These agree with the 

 numerous thin hard tabular pieces of sandstone found scattered over 

 the surface of the ground around Apchurch near Sittingbourne. 

 On the hill above Stiiford Bridge, Essex, where the lower tertiaries 

 were cut through, there are' a few blocks of pudding-stone. In the 

 neighbourhood of the conspicuous tertiary outlier at Cobham near 

 Gravesend, large mammillated blocks of siliceous sandstone are com- 

 mon on the chalk hills. Blocks of a larger size, but more even- 

 surfaced, abound on the downs above Maidstone ; they are also 



* The remarkable and thick trail of sandstone blocks in the valley of rocks near 

 Marlborough is well known. Many other valleys in that district, as those to the 

 south of East and West Kennet, Dean, Clatford, and others, exhibit the same 

 phsenomena, although not on so large a scale. The hills on the sides and at the 

 heads of these narrow vales are also strewed over with numerous detached blocks. 



t At Walter's Ash and Napple Common ; they are equally abundant on Denner 

 Hill, three miles west from Great Missenden. 



