S'RKSTWICH WOOLWICH AND READING SERIES. 121 



as in the other freshwater species, the distinction between the older 



and the newer forms is remarkably small, a fact which can be readily 



understood when it is considered how many of the Woolwich species 



were originally identified with species of the Upper Eocene fluvio- 



marine beds of the Isle of Wight. The representative fonms of these 



two periods present, in fac^t, a remarkable and close analogy. 



(s) Three varieties of the teeth of Lamna are found, two of them bearing 



a close resemblance to these two London clay (Sheppey) species, but 



they do not seem to me to be quite identical. They may, however, 



only be varieties. 



In addition to the fossils of the foregoing list, the following species have 



been quoted from Woolwich upon the authority of the early numbers of the 



• Mineral Conchology,' but, I believe, in error, which has been partially 



corrected in a later index. 



Cyrena (Cyclas) obovata, var., Min. Con. pi. 162. figs. 4 to 6. Confined 



to the Middle and Upper Eocenes of Hampshire. 

 Fusus (Buccinurn) labiaius, Min. Con. pi. 412. figs. 1, 2. Confined to the 



Middle and Upper Eocenes of Hampshire. 

 Melanopsis fusiformis, Min. Con. pi. 332. figs. 1 to 7- Confined to the 



Middle and Upper Eocenes of Hampshire. 

 Neritina concava, Min. Con. pi. 385. figs. I to 8. Confined to the Middle 



and Upper Eocenes of Hampshire. 

 Potamomya (Mya) plana, Min. Con. pi. 76. fig. 2. Confined to the 



Middle and Upper Eocenes of Hampshire. 

 Fusus costatus jS. {Murex rugosus, Park.), Min. Con. pi. 199. fig. 2. Con- 

 fined to the Crag. 

 The Rev. H. M. De la Condamine has also given, in his paper before re- 

 ferred to, eight species of shells and one of Lamna from Woolwich and 

 Blackheath not in the above list, and which, I think, he will now agree 

 vi'ith me have been introduced by some eiTor in the specific determinations 

 which it is desirable to correct, in order to prevent, as is the case with the 

 above, any confusion, or difficulty to subsequent observers. 



The Corbula revoluta, Sow., has been quoted from Heme Bay. It 

 should be confined to Barton and Hampshire. 



§ 4, Lithological Structure. 



It happens with this, as with the preceding chapter, that the de- 

 scriptions of the several local sections embrace the mention of almost 

 all the varieties of mineral character presented by this group, and 

 render it therefore unnecessary to give more than a general summary, 

 and to allude to a few special points of inquiry : of these may in par- 

 ticular be instanced the origin of the Druid sandstones of Marl- 

 borough Downs and Salisbury Plains, and of the Hertfordshire 

 Pudding-stones. 



Viewed as a whole, the ^Voolwich and Reading series consist, 

 1st, of mottled clays, tenacious, free from carbonate of lime, and 

 with a prevailing red base ; 2nd, of sharp light-coloured quartzose 

 v«aud, more or less mixed with green sand and with flint-pebbles. 

 These two component parts usually form distinct and separate beds, 

 extremely irregular in their range and development ; the clays })re- 

 vailing almost to I he exclusion of the sands in (he Isle of Wight and in 

 part of the Hampshire district, and the sands increasing as the group 

 ti-ends through Wiltshire, Berkshire, and Surrey, but thick-bedded 



