254 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 23, 



series tlie equivalent, and to wliicli precise portion of the former is 

 the Ostrea Bellovacina bed of the latter to be referred ? what portion 

 of the Isle of "Wight strata represents the fossiliferous conglomerates 

 of the neighbourhood of Bromley, and the extensive pebble-beds of 

 Blackheath and iVddington ? and of what portions of the Heme Bay- 

 section are all the above-mentioned strata individually and jointly to 

 be considered the representatives- — if represented at all ? The rela- 

 tive position of the Northaw " Ostrea'' bed, and of the Kyson bed 

 with its remains of the Monkey, in reference to those above men- 

 tioned, is also to be determined. 



I am aware that the series of mottled clays at Reading with their 

 overlying seam of marine shells, has been referred as a whole to the 

 series of sands, clays, and pebbles at AYoolwich and Charlton, the ma- 

 rine upper bed at the former place being viewed as the representative 

 of the fluviatile and estuary beds of the two latter ; the thin but uni- 

 form stratum of impure green sand with large flints, which in both lo- 

 calities immediately overlies the chalk, at Reading with, and at Wool- 

 wich without, the Ostrea Bellovacina, being considered synchronous. 

 It is true, that the series in each of these localities bear on a broad 

 scale the same relative position to the chalk and the London clay ; 

 but, this admitted, it remains to be ascertained whether the whole of 

 these series belong to one and the same group, occupying in an irre- 

 gular manner this space in geological time, and varying in its thick- 

 ness, in its mineral character, and in its organisms, without deter- 

 minable order ; or whether there are not subdivisions, each traceable 

 over certain areas, and exhibiting essential modifications in structure, 

 but yet invariably holding the same relative position one to another, 

 and which may lead to the estabhshment of a more connected order 

 and definite sequence in the phsenomena. In this iaquiry, we must 

 take into consideration the physical condition of the surface at that 

 early Eocene period, and ascertain how far it is probable that, as with 

 the more recent London clay, which spreads uniformly over the whole 

 area, the several and distant beds in this lower series originated in 

 one sea, and were therefore likely to extend over co-extensive areas. 

 The determination of this point is of material importance to the 

 question of exact synchronism of the strata. 



In the Isle of Wight and in the tertiary district westward of Lou- 

 don, the London clay consists of tenacious brown and bluish-grey 

 clays with layers of septaria, usually most abundant in the browner 

 clays, and with small round black flint pebbles occasionally scattered 

 through some of the darker and more sandy portions of the clay. Im- 

 mediately at its base the London clay commonly contains a greater 

 or lesser admixture of green and yellow sands, generally mixed with 

 rounded flint pebbles, and not unfrequently cemented by carbonate 

 of lime into semi-concretionary tabular masses. These mixed beds 

 however never exceed a few feet in thickness, and pass upwards 

 rapidly into the great mass of the London clay, to which they appear 

 to be subordinate, being clearly and sharply separable from the sands 

 and mottled clays both in mineral and zoological characters. (See 

 Sections 1 to 6.) To the east\^-ard of London, as at New Cross, 

 Upnor, and Heme Bay, the mass of the London clay is apparently 



