452 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Juiie 5, 



it to the surface only. To what distance right and left of the railway 

 it extends I have not yet been able to learn, but it is evidently very 

 considerable. This however is certain, that whereas it was deposited 

 subsequently to the great portion of the black peaty soil, it has been 

 again covered up by a subsequent deposition of the same black sub- 

 stance. 



On washing out the marl I found a considerable number of land 

 and freshwater shells, of existing species. The following T have 

 already found : — 



Helix pulchella, Muller. Planorbis Isevis, Alder. 



Limnseus stagnalis, Drap. Bithynia tentaculata, Linn. sp. 



pereger, Drap. (two varieties). Physa fontinalis, Drap. 



Planorbis marginatus, Drap. Valvata cristata, Muller. 



vortex, Muller. Pisidium pusillum, Turton, sp. 



earinatus, Muller. obtusale ?, Lamarck, sp. 



Innumerable seed-vessels of Char a {Gyrogonites) ; and numerous 

 Entomostraca^ , among which are Cypris minuta, Baird; C. auran- 

 tia, Jurine ; C. setigera, Jones ; C. gibba, Ramdohr ; Candona lu- 

 cens, Baird ; and Candona reptans, Bairdf . 



We have thus evidence of the alternation of two freshwater depo- 

 sits of different characters ; and it becomes an interesting subject of 

 inquiry, whence the white marl was derived of which one of the de- 

 posits consists. I supposed it was derived from the chalk brought 

 down by the various rivers which from the surrounding hills flow into 

 this low district, but neither Dr. Mantell nor Mr. Bowerbank, who 

 have obligingly examined it, have been able to detect any remains of 

 the Microzoa which abound in that formation, and would probably 

 have remained uninjured had the white marl been derived from that 

 source. 



That the whole of this district has been covered by the water of 

 the sea previous to the draining to which the country has been sub- 

 jected, and probably at no very distant period, has always been ad- 

 mitted| . A very slight oscillation in the level of this tract of coun- 

 try would have the effect of raising it for a time above the influence 

 of the highest tides, and thus a portion of the district may have been 

 temporarily converted into a freshwater lake or marsh. The abun- 

 dance of the stems and seed-vessels of Chara shows that it must have 

 been for a long time protected against all marine irruptions ; and the 

 great abundance of the fossil shells in all ages of growth proves that 

 they were not merely washed into the basin, but that the district 

 must have been for a considerable space of time covered by fresh water. 

 I am aware of the meagreness of this account, but I thought the fact 

 alone, as adding to our knowledge of the successive deposits of the 

 surface of our own country, sufliciently interesting to justify my laying 

 these observations before the Society. 



P.S. Since the above notice wa^ read I have received the following 



* For the examination and determination of these minute fossils I am indebted 

 to the kind attention of our curator, Mr, T. Kupert Jones, 

 t See Ann. Nat. Hist. ser. 2. vol. vi. p. 28. 

 % Ansted's Geology, vol. ii. p. 499. 



