1868.] PRKSTAVlcn— RED CRAG OF SUFFOLK. 461 



the hollows between them, and occupying a similar, and sometimes 

 a rather lower level than the summits of these older reefs. It forms 

 such an extremely vaiiablc series of beds, that the author has been 

 unable to observe any definite order of succession in the greater part 

 of it; but he remarks that oblique lamination is most strongly de- 

 veloped in the lower and central portions, and that almost every- 

 where there occurs at the base a bed of phosphatic nodules, although 

 deposits of that nature are by no means confined to one level. Old 

 sea-cliifs of Coralline Crag, and remains of old sea-beaches at their 

 base, are described by Mr. Prestwich as occurring at Sutton ; and 

 he also gives detailed descriptions of the numerous pits in the Red 

 Crag of Suffolk where the phenomena which he describes may be 

 observed. Dividing the Red Crag into an upper, frequently unfos- 

 siHferous member (the fossils of which, being most frequently in the 

 position in which they lived, may be regarded as truly representing 

 the fauna of the period), and a lower, fossiliferous portion (in which 

 the shells are found mostly in a broken and comminuted state, and 

 mixed largely with fossils derived from the older Coralline Crag), the 

 author describes their distribution in Suffolk, and their mode of 

 occurrence on the eroded Coralline Crag, referring more especially to 

 the difficulty in drawing the line between them in many cases. 



In treating of the organic remains of the Red Crag, Mr. Prestwich 

 gives lists of the shells found at the different localities, which had 

 been prepared with the aid of Mr. Gwyn Jeffreys. Taking the local 

 conditions into consideration, eliminating the extraneous fossils of 

 the Red Crag of Sutton, Butley, <fec., and excluding the freshwater 

 fossils of the more northern districts, the author regards the re- 

 maining fossils of the two divisions of the Red Crag as being so 

 closely related that the whole group must palaeontologically be 

 treated as one. Mr. Searles Wood has given the total number of 

 species of its Mollusca as 239 ; to these Mr. Gwyn Jeffreys has 

 added six additional species ; on the other hand, he regards ninety- 

 nine of them as varieties and extraneous fossils, leaving 146 species 

 belonging to the Red Crag. Of these Mr. Jeffreys has identified 

 133, or 92 per cent., with living species, 115 still being inhabitants 

 of British seas, 15 being found in more northern seas, and 3 in more 

 southern. 



From the Mammaliferous Crag of Norfolk and the Red Crag of 

 Suffolk never having been found in superposition, from the circum- 

 stance that just at the point where the latter ceases the former 

 begins, as well as from the community of so many species of organic 

 remains, the author regards the two deposits as equivalent ; and he 

 attributes their distinctive characters partly to the extraneous fossils 

 in the Red Crag, and partly to the difference in the conditions which 

 prevailed in the two areas at that time, and especially to the more 

 littoral and brackish-water conditions which prevailed in the Norfolk 

 area. In conclusion, Mr. Prestwich gives a sketch of the physical 

 history of the Red-Crag period, describing the mode in which the 

 various phenomena which he notices have been produced. 



