726 ME. F. W. HAEMEE ON THE CRAG OF ESSEX. [Nov. I9OO, 



not then arctic. 1 Moreover, the Forest-bed flora, as Mr. Eeid has 

 told us, was similar to that of Norfolk at the present day. 2 



On the contrary, the Leda-myalis Sands, which contain also Astarte 

 borealis, seem naturally to group themselves with the Arctic Fresh- 

 water Bed, as belonging to the same epoch and originating under 

 similar climatal conditions. Both should be regarded, I think, as 

 Glacial, rather than as Pliocene. 3 



IV. The Derivative Mollusca of the Eed Crag. 



"Whether or no any considerable proportion of the Eed Crag 

 mollusca have been derived from older formations, is a question upon 

 which much difference of opinion has existed. Both Searles Y. 

 Wood 4 and his son, 5 as well as Prestwich, believed that many Eed 

 Crag shells were extraneous (the lists of such forms given by them 

 having, however, little in common) ; Prestwich, indeed, expressed 

 the extreme opinion that all species which occur in the Eed but not 

 in the Norwich Crag are so. 6 



While a few forms characteristic of horizons older than the 

 Coralline Crag may be derivative, possibly from submarine shell- 

 banks of Older Pliocene age then existing in the Eed Crag sea, 

 I do not now think that the Eed Crag fauna has been leavened with 

 an admixture of Coralline Crag species. There are Miocene shells 

 which still live in the North Sea, and it seems more probable that 

 some Coralline Crag mollusca may have lingered on there until Eed 

 Crag times, than that any specimens should have been washed out 

 of the former deposit into the latter. We have no positive evidence, 

 moreover, that such has been the case. It is not at Tattingstone, 

 Eamsholt, or Sudbourn, where the Eed Crag rests upon, or against 

 the Coralline Crag, or at the stack-yard pit near Shottisham Creek, 

 where fragments of indurated Coralline Crag are embedded in the 

 former, that such specimens are so frequently met with, as in the 



1 During the Weybournian Period there may very probably have been con- 

 siderable accumulation of snow and ice on the Swiss highlands, the melting of 

 which, when the climate became milder, would produce, especially in spring, 

 sudden and violent floods. Animals frequenting the low pasture-grounds 

 bordering the Forest-bed river and its tributaries would thus be annually caught 

 and swept away. In this manner only can we explain, I think, the presence, in 

 so limited an area, of such enormous quantities of mammalian remains. It may 

 be worth noticing that they seem to occur in beds deposited on the convex side 

 of one of the great bends of the Forest-bed estuary, that is, from Kessingland in 

 Suffolk to Cromer (they are not found, so far as we know, at any great distance 

 inland), where the heaping-up of sediment and wreckage would naturally take 

 place. 



2 Mem. Geol. Surv. (1890) ' Plioc. Beds of Britain' p. 185. 



3 Mr. Reid seems inclined to separate the Leda-myalis Sands from the Arctic 

 Freshwater Bed, regarding the one as Pliocene and the other as Pleistocene. 

 The introduction of the latter term was, I have always considered, a mistake. 

 It is not, however, so objectionable as Quaternary. 



4 Quart. Journ. Geol. Soc. vol. xv (1859) p. 32. 



5 '3rd Suppl. Monogr. Crag Mollusca' Pal. Soc. (1882) p. 19. 



15 Quart. Journ. Geol. Soc. vol. xxvii (1871) p. 350. Prestwich evidently 

 felt that this argument cuts both ways, and he consequently regarded all Red 

 Crag forms which occur also at any other later horizon, as in what were then 

 called the Sables jaunesof Belgium, or in the Glacial beds, as being proper 

 t-o the Red Crag, and not derivative. 



