Yol. 56.] MR. F. W. HARMER ON THE CRAG OF ESSEX. 717 



Foulton Hall, Little Oakley, midway between Beaumont and 

 Harwich (about 4 miles from each place), a shallow section (No. 5 

 in the map, fig. 1, p. 710), showing only 1 or 2 feet of dirty-looking 

 horizontally-bedded Crag, which, although its existence was known 

 both to S. Y. Wood, Jun., 1 and to Mr. Whitaker, 2 had received 

 hitherto no attention from collectors. It has revealed, however, an 

 exceedingly rich and interesting fauna, generally similar to that of 

 Walton and Beaumont, and distinctly southern. This fauna includes 

 nevertheless a larger proportion of northern forms than is found 

 at those places, representing the somewhat later period before the 

 southern shells had commenced to disappear, when boreal mollusca 

 were beginning to establish themselves, in greater or less abundance, 

 in the Pliocene basiu. 



As the Crag of Little Oakley appeared to be different in age from 

 anything previously known, I determined to work it out as thoroughly 

 as I could. By the kindness of Gilbert Purvis, Esq., of Foulton 

 Hall, I was allowed to excavate and sift over an area 10 yards in 

 length by 3 in breadth, obtaining in so doing more than 350 

 species and well marked varieties of fossils, 3 some of them new to 

 science, and many of them known to Wood from the Coralline Crag 

 only. 4 The presence of so large a number of distinct forms in one 

 seam, little more than 12 inches thick, and only 10 yards long, 

 constitutes a striking illustration of the extraordinary richness of 

 the molluscan fauna of the North Sea at that period. 5 



Among the boreal forms present at Oakley I may mention : — 

 Trophon scalar if or mis, Tr. (Sipho) gracilis, and its allies Tr. Olavii, 

 Tr. gracilis var. convolutus, Tr. Sarsii, Tr. Jeffreysianus, and 

 Tr. islandicus, and Trochus formosus, which are all more abundant 

 there than they are at Beaumont, as are also Natica clausa, Mactra 

 obtruncata* Tellina obliqua, and T. prcetenuis. The northern shells, 

 Trojohonbarvicensis, Admete viridula, Scalaria groenlandica, Modiola 



1 MS. 1-inch map in the Geological Society's Library (about 1864). 



2 Mem. Geol. Surv. (1877) ' Walton-Naze & Harwich' p. 14. 



3 The occurrence, or otherwise, of so-called varieties at the various Crag 

 localities is of* considerable importance, and should always be noted. For 

 example, Pitrpura lapillus is said to occur at all horizons of the Upper Crag, but 

 the variety specially characteristic of the Oakley bed [at present undescribed, 

 but which I propose to call intermedia] is very different from the existing shell, 

 while that of the much more recent Norwich Crag is identical with it. The 

 distinction between species and varieties is, moreover, quite arbitrary. Many 

 so-named varieties of Crag species, as, for example, those of Nassa reticosa, 

 differ more widely one from the other than do other Crag forms which are 

 generally regarded as specifically distinct. 



4 The Crag-pit at Foulton Hall is no longer available : I was compelled to 

 level it down as the work proceeded. I shall be pleased, however, to show my 

 specimens to any student of the Crag, and I propose eventually to place them 

 in the Museum at Norwich. 



5 The present molluscan fauna of the North Sea is much poorer than this. 

 During a recent visit to the shell-beaches of the Dutch coast, I noted less than 

 30 species, and not more than about 100 have been recorded as now living 

 near the shores of Norfolk, many of them being very rarely met with. 



e Mactra obtruncata is abundant in the upper part of pit No. 4 at Beaumont. 



