PRESTWICH WOOLWICH AND READING SERIES. 129 



of concretionary sandstones in the sections and cuttings of the Lower 

 Tertiaries. In the Bagshot Sands themselves they are confined to a 

 comparatively small range of country, and even in that district I have 

 never seen them in sand-pits or road -side cuttings. They are sought 

 out specially at a few spots on the hills hy dipping iron rods into the 

 sands. Again, although at and near London the Lower Tertiaries 

 so often contain subordinate concretionary or conglomerate rocks, 

 how rarely do such masses show at their outcrop : at Sundridge only 

 are some of these latter beds worked. 



The flint-gravel which caps the hills around Newbury contains a 

 few rather large specimens of the harder sandstones, but the gravel 

 of that system of valleys which wind down from the chalk hills on 

 the north-west of Newbury abounds with such blocks, together with 

 a good many large blocks of the more saccharoid and softer stones. 

 The course of this drift is towards, aiid not from, the area of the 

 Bagshot Sands ; and as we have no proof of the extension of this 

 formation over the Chalk Downs, whereas we know that detached 

 outliers of the Lower Tertiary sands extend far over those hills, we 

 should expect to find, in the drift, the debris derived from the latter 

 and from the chalk, and not from the Bagshot Sands. Whence 

 also, as well as from their association, I am inclined to consider that 

 both descriptions of sandstones are derived from the Lower Tertiary 

 sands. 



Further, admitting the fact of an occasional and local consolidation 

 of the sand beds of the Lower Tertiaries, we have an h-priori 

 argument in favour of the whole group of the Druid Sandstones of 

 Wilts, Hants, Bucks, and Kent, and of the Pudding-stones of Herts, 

 being derived from this source, from the circumstance that the 

 lithological structure of each variety is respectively in accordance 

 with the mineral components forming the strata in the immediate 

 vicinity of the places where these rock-blocks are found ; i. e. that 

 the concretionary stone in each case represents the component parts 

 of some portion of the adjacent "Woolwich and Reading series," 

 with the difference that they are consolidated. 



This conclusion is corroborated by the very definite and distinct 

 proofs furnished by the cliffs of St. Marguerite near Dieppe. We 

 there find the Woolwich fluviatile clays with the Cyrena cuneiformis, 

 Melania inquinata, and Cerithium variabile underlaid by a bed 

 of whitish quartzose sand reposing upon a very uneven siirface of 

 the chalk. The section is between one and two miles in length, 

 although it is only near the lighthouse (le phare d'Ailly) that the 

 fluviatile beds exist. These sands contain in several parts of the 

 section subordinate blocks of a white saccharoid concretionary sili- 

 ceous sandstone, which is worked to some extent, and afi'ords masses 

 frequently measuring many feet in length. These sandstones also 

 often contain, like the Druid sandstones of Wilts, rolled flint-pebbles 

 and subangular flints. As these beds are evidently a prolongation of 

 the Woolwich beds on the Sussex-district type, the phsenomena thus 

 exhibited in the neighbourhood of Dieppe may fairly be admitted 

 in collateral proof of the argument with respect to the origin in this , 



VOL. X. PART I. K 



