1847.] PRESTWiCfi ON THE BAGSHOT SANDS. 395 



this avails little, as the remains of plants yet found there are far too 

 indistinct for the remotest determination, but with the Lower Bag- 

 shot sands it serves to establish a coniiexion rather important in kind 

 although wanting in strength. 



When the Loiver Bagshot sands are entirely arenaceous no distinct 

 traces of plants exist, but where the sands contain subordinate foliated 

 clays, as in the neighbourhood of Woking, and more especially of 

 Chertsey, these clays usually exhibit numerous small and generally 

 indistinct vegetable impressions. In the more important stratum of 

 this description immediately underlying the green sands, and which is 

 worked to some extent in brick-fields about Addlestone, Chertsey and 

 Otter, larger and more perfect specimens may be occasionally ob- 

 tained*. 



The matrix in which these impressions of plants are preserved is 

 of a very similar character and appearance both at Alum Bay and in 

 the Bagshot district ; only in the latter it is usually coarser and mi- 

 caceous, and does not show the impressions so sharply. The Bagshot 

 specimens are also very difficult to preserve ; the clay laminating and 

 falling to pieces as it dries. I am not aware that any of the species 

 from Alum Bay have been figured. Some of them somewhat resem- 

 ble some of the species of Phyllites and Cidmites from the Calcaire 

 grossier described and figured by Adolphe Brongniart in Cuvier and 

 Brongniart's Geology of the neighbourhood of Paris, but I have not 

 been able to establish any good identity f. I can only therefore refer 

 to the plants found in the Bagshot sands as a group, and state that 

 a comparison of specimens with those found at Alum Bay shows 

 that they are of analogous forms and preserved in a m^atrix of similar 

 lithological character. The most abundant species is a long lanceo- 

 late smooth-edged leaf; another species of like form has the edges 

 dentated. 



Conditions of Structure and of Organic Remains. 



We have now described the main points connected with the struc- 

 ture and organic remains of the Bagshot sands. Their regular stra- 

 tification and persistent lithological structure are apparent. They form 

 a separate group in the Eocene period, distinct from the London clay 

 both in the character of its fossils and in their mineral composition. 

 In this latter however they have many points of resemblance with, the 

 sands under the London clay, as in their blocks of concretionary sand- 

 stone, their beds of sand with layers of round fiint pebbles, which 

 have frequently led to such beds being mistaken for a part of the 

 Plastic clay series. 



Notwithstandhig the great scarcity of organic remains, I am led to 



* The best specimens I obtained from Botley, tbvee miles W.S.W. from Chertsey. 

 These pits have not however been worlced for four or five years past, and the sec- 

 tion is no longer visible. 



t Some of the specimens resemble those figured by Dr. Mantell in his 'Geology 

 of Sussex,' from the Plastic clay of Newhaven. The few species found there have 

 hardly sufficient character to complete a comparison. As a group they are certainly 

 distinct. Besides, those of Newhaven are in beds below the London clay, and those 

 of Alum Bay occur in strata above the London clay. 



VOL. HI. PART I. 2 E 



