APPENDIX. 305 



Mr. Pickering has furnished me with those from Grays and the Kennet Valley ; Mr. Woodward has 

 supplied the Maidstone one; and the Cropthorn list was published by the late Mr. Strickland. The 

 species from Clacton and Stutton were obtained by myself, and for which I am responsible. 



Land or fresh-water shells have also been found at Bacton (a), Brentford, Cambridge (J), Casewick, 

 Charing (5), Chislet, Clapton, Cuxton (£), near Stroud, Erith, Faverskam, Folkestone, West Hackney, 

 Harwich, Hemingford Abbots, Heme Bay, Ilford, Isle of Wight, Littleport (6), (Isle of Ely), Market 

 Weighton, Mundesley, Peterborough, Rain near Braintree, Ruiiton, Stamford, Valley of the Nar (b), 

 Witham, and Yeovil ; perhaps elsewhere, but the localities are too numerous to have here a separate and 

 distinctive catalogue. (c) These Lacustrine or Fluviatile Beds appear to be principally'confined to the middle 

 and southern portions of England ; and although they may, perhaps, exist in Scotland or in Ireland, I 

 have been unable to procure, for insertion here, the name of any locality that might be considered as 

 analogous or synchronous with the older of these deposits. The fresh-water fossils that have come under 

 my observation from either of those kingdoms, or from the Isle of Man, were found in peat bogs. 



By the following table it will be seen that the species of fresh-water shells fall short of those which 

 live exclusively on land, although the individuals of the former generally outnumber those of the latter, 

 as we see amongst the same group of Mollusca of the present day. In the Uppermost Tertiaries we have 

 about fifty-five species of land shells, with about forty-four fresh-water ones. In the latter are included eleven 

 species of Bivalves, and the amphibious Succinea. Our catalogues of the land and fresh-water Mollusca 

 existing in England enumerate about seventy-two of the former, with fifty-one of the latter, giving a slight 

 difference in the proportions between the recent and fossil species ; but the excess in number at the present 

 day is greater than can be made up by the extinct species of these deposits, showing that, if we really have 

 obtained all the species belonging to those past periods, the incomers exceed those which have here gone 

 out of existence, giving a considerable increase to the existing Fauna, making the insular condition of 

 England better tenanted than when it is supposed to have formed a part of the Continent. 



(«) Bacton is considered by Mr. Prestwich (from position) to be the oldest of all these fresh-water 

 deposits ; it is most probably synchronous with the Marine and Estuary Beds of Chillesford and Bramerton. 

 I much regret my list of Mollusca from this locality is so insignificant as to be unworthy of a separate 

 insertion. Chislet, Ilford, and Mundesley contain one or more of the extinct species, and these may be 

 assigned to the age of Stutton, Grays, &c. 



(b) These are probably the most modern. 



(c) The uppermost Tertiaries, or those above the Crag in these islands, have, with every degree of 

 probability, been separated into four distinct Geological Periods, and our able coadjutor, Mr. Prestwich, 

 has, I believe, come to the conclusion that an addition must even be made to this number. Their separa- 

 tion has, however, been founded exclusively upon geological evidence ; and it is with the hope that palseon- 

 tological aid may afford some slight assistance to their correct determination that I have made a separate 

 enumeration of the contents of several of our most important fresh-water localities. Existing species cer- 

 tainly extend through all, but they are not equally disseminated. 



The want of permanence presented by the more recent Formations in the duration of the specific 

 existence of their Fauna, compared with those of more ancient Deposits, is probably owing to the greater 

 variety and more rapid alterations of the conditions under which the organisms have their existence in recent 

 epochs than in those more remote. 



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