566 Robet't O. Bell — Notes on Pliocene Beds. 



been very great in the East Anglian area during the Pliocene period ; 

 the species quoted above are a few examples among many which 

 exhibit these alterations. Do not such facts imply that a much 

 longer time than is generally allowed, is necessary to account for 

 the variation and extinction of species, which occurred during the 

 formation of the Crags ? 



At Walton-on-the-Naze, the Eed Crag is shown (as the late Mr. 

 Searles Wood always insisted) in its earliest and purest condition ; it 

 is the most instructive section at present visible, and contains by far 

 the largest number of species, especially of Mollusca, of which about 

 235 have been recorded up to the present time ; yet many of the 

 genera of the older Crag, particularly those of southern habit, are 

 absent, and others exist only in a dilapidated or fragmentary state. 



An examination of the deposit shows that it was formed in a 

 shallow depression of the London Clay, in the central and deepest 

 part the Crag beds being almost horizontal and undisturbed. Here a 

 number of Pectunculi may be found, with their valves united, and in the 

 position in which they lived and died. Just above this bed the 

 large Almond Whelk, Fusus antiquus, makes its first appearance in 

 geological history, and so far as evidence is concerned this seems to 

 have been its birth-place ; it comes in as it were with a rush (as at 

 a much later date did Tellina BaltMca), the deposit at this spot being 

 full of them in the finest and most perfect condition. 



The appearance of this shell in our Pliocenes may be taken as one 

 of the best indications of the great change of climatic conditions 

 which had occurred since the close of the Coralline Crag ; it may be 

 seen in plenty in the Eed Crag beds overlying the Coralline at 

 Sutton (the best and almost only instance where the superposition 

 can be seen) ; but it has never been observed in an earlier deposit, 

 either here or on the Continent. 



Another striking evidence of change of condition in the East 

 Anglian area is that this shell is the first and best representative of 

 a family or section (Neptunea) of the old Linnasan genus Murex, which 

 is almost exclusively confined to the Boreal and Arctic regions of the 

 world. Not only this species, but the whole of this particular section 

 (if the doubtful subgenus Sijjlio is excepted) had, so far as has been 

 ascertained, no previous existence to Eed Crag times, since which 

 period it has continued with undiminished vitality, and in recent 

 seas it is as plentiful in suitable places as formerly, and exhibits still 

 more variety than in the limited Crag area. 



The sculpture of the earliest form agrees in its fine striation with 

 that almost universal with these shells round the coasts of Great 

 Britain, and more particularly with those on the sandy flats round 

 the mouth of the Thames. Only in St. George's Channel ofi' the 

 Irish coast does the carinated variety occur in any number. Several 

 other northern forms of Mollusca have been found here at various 

 times, some quite recently, as Fusus Islandicus (Chemnitz), and it 

 would seem to point to the existence there of one of those old boreal 

 outliers mentioned by Edward Forbes as among the indications of 

 a former glacial climate. 



