54 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



work, such as Cerithinm reticulatum, which is very abundant in this 

 deposit, and it omits several* which I have not seen. 



Taking the assemblage as it is here given, and in conjunction with 

 what has been said respecting the deposit itself, we may infer, from 

 the circumstances of position of the Pholas crispata, that the relation 

 of the land to sea-level was then, for this spot at least, much what it 

 is now, or that these ledges in which it is found, then lay, between 

 tides, on a coast-line. The Pecten polymorj^hus, which occurs in 

 the sand filling the cavities of the Pkolades and in other sands 

 immediately above, belongs, when living, to a sea-zone deeper than 

 that occupied by Pholades, and ranging from 10 to 12 fathoms; in 

 these sands it is met with only in detached valves, and must have 

 been washed up from a lower to a higher zone. 



Subsequently to the condition of coast-line here indicated, some 

 change must have happened which caused the same spot to be in- 

 cluded within an area admitting only of the tranquil deposition of 

 mud and silt. Many of the bivalved molluscs of the foregoing list 

 lived in and on this mud, as is evident from the positions in which 

 the shells are now found, more particularly the Myce, Lutrariee, and 

 PuUastrcB {Tapes) ; or the whole of this assemblage of shells, as well 

 as the composition of the beds containing them, indicates that this area 

 became an enclosed salt-water lagoon, so that the list must be con- 

 sidered as a special one, — the result of local conditions subordinate 

 to, but also clearly indicative of, a much larger marine fauna, which 

 had its full development in some adjacent sea. We may further 

 fairly presume that this fauna, as a whole, differed as much from that 

 of the present Channel waters, as the fossil contents of the Selsea 

 "mud deposit" do from the MoUusca now inhabiting the series of 

 large creeks and lagoons extending from Fareham to Pagham. 



It will be seen from the notices appended to the several species, 

 and which have been carefully compiled with reference to their dis- 

 tribution, that the character of the whole assemblage is essentially 

 Southern and Western ; that some of the species, for instance, are 

 such as abound on the rocks and in the bays of the Channel Islands, 

 but others hardly reach beyond Torbay on our own coasts. Some 

 which are now found on the Sussex coast do not seem to range 

 further, or into the German Ocean area. This southern relation of the 

 fauna of the lower Selsea deposit is further very strikingly illustrated 

 by the presence of the two very remarkable and abundant forms, 

 Pecten polymorphus and Lutraria rugosa, neither of which, at pre- 

 sent, are to be found ranging further north than Lisbon. 



We seem therefore to have indications, 1st, of a warmer condition 



* Pholas Candida, Lutraria arenaria ?, Cardium fasciatum, Rissoa varia ?, 

 Trochus cinereus? [is not this the young of T. millegranus or striatus ?'\, Pur- 

 pura lapillus, Helix nemoralis, H. hortensis, Assiminia Grayana, Bulla hydatis. 

 Great care is necessary in collecting the shells from the lower mud-deposit, par- 

 ticularly on the Bracklesham Bay side, as recent species or such as belong to the 

 present coast, together with shells of the nummulitic series, become imbedded in it 

 on the surface. I entertain some doubt whether Nassa reticulata and Fusus turri- 

 culn should have been included. I have no doubt, however, but that the list will 

 ultimately be considerably enlarged. 



