Yol. 56.] MR. F. W. HARMER ON THE CRAG OF ESSEX. 707 



the Scaldisian zone of Belgium, for example, with its southern 

 fauna, representing one portion of it, and the Amstelian of Holland, 

 in which arctic shells occur, another. It seems desirable, therefore, 

 while retaining it for general use, to adopt for its various horizons 

 some more definite and distinctive names. In a paper read before 

 the British Association at Dover, in 1899, published in abstract 

 only, I proposed the classification tabulated on p. 708 for the Pliocene 

 deposits of the East of England. 



The Coralline Crag (Gedgr avian 1 ) has been hitherto referred 

 to the Older, and the Red Crag, including the Walton zone, to the 

 Newer Pliocene period, the former being regarded as equivalent to 

 the Plaisancian deposits of Italy. 2 



At the time of the publication of Wood's Supplement in 1872, 

 there seemed good reason for this classification, as more than one- 

 half of the species known from the Coralline Crag had not then 

 been found in the Red, but a large number of these have since 

 been obtained from the latter (50 by myself during the last three 

 years at Beaumont and at a new locality at Little Oakley, in Essex) ; 

 and increased knowledge of these formations has always tended to 

 diminish rather than to emphasize the distinction between them. 



Most of the characteristic Coralline Crag species are now known 

 to occur in the Waltonian Beds, the exceptions being principally 

 either forms which are rare or unique in the Coralline Crag, or small 

 shells that might have been brought from some distance into the 

 Crag area by currents from the south, which I think prevailed at the 

 earlier period. The principal difference between the Coralline and 

 Walton horizons is that the Waltonian Beds contain a number 

 of mollusca which, during the interval separating the two periods, 

 had invaded the Crag basin, presumably from the north, owing 

 probably to the opening-up of communication with northern seas by 

 the tectonic movements referred to in my former papers. 3 A 

 reference to the synoptical analysis on p. 725 will show that palse- 

 ontologically there is not more difference between the Coralline 

 and Walton Crags than there is between the latter and other 

 later zones. I doubt therefore whether the Coralline Crag is as 

 old as the Plaisancian, 4 and am inclined to draw the line separating 



1 Gedgrave is the only locality in the Crag district where none but Coralline 

 Crag deposits occur. 



2 See, for example, C. Eeid, ' Pliocene Deposits of Britain ' Mem. Geol. Sury. 

 (1890) p. 223. 



3 With one or two exceptions, the Red Crag forms unknown from the 

 Coralline Crag cannot be regarded as modified descendants of species belonging 

 to the latter, and they must therefore have emigrated from other seas. Some 

 of these, however, had reached the Belgian area as early as theDiestian Period : 

 as, for example, Nassa reticosa, Natica hemiclausa, Astarte obliquata, and 

 Telliva Benedenii. Mr. P. F. Kendall informs me that he has found a specimen 

 of Nassa reticosa, in the Coralline Crag at Gedgrave. 



4 Even allowing for the difference in latitude, the correspondence between the 

 fauna of the Coralline Crag and that of the Plaisancian does not seem to me 

 to be very close. From time to time I have made collections from the latter at 

 Bordighera, Cannes, Biot, etc.; but I found that comparatively few of the fossils 

 so obtained, presumably the characteristic forms of these deposits, are known 

 from the Coralline Crag. 



3b2 



