Alfred Bell — Age of the Suffolk Boxstones. 15 



III. — The Stjitolk Eoxstones and thkik probable Age. 



By Alfred Bell. 



(PLATES III AND IV.) 



rpHE detrital matter \inderlyiiig the Suffolk and E.W. Essex 

 1 Crags forms an incongruous mass of disrupted local rocks and 

 fossils, supplemented by a few transported boulders of igneous and 

 sedimentary rocks of different ages and mostly small. To these have 

 to be added organic remains of many classes in various conditions of 

 preservation. 



The bulk of this miscellaneous assortment consists of clays and 

 sands metamorphosed by phosphatization and other agencies, "whose 

 fossils indicate two or more distinct horizons ; to place these in their 

 proper geological positions it is requisite to see what relations they 

 bear to those of the deposits, or strata, above and below, and to 

 consider the causes that brought them into their present position. 



The area occupied by this detritus is exceedingly limited, not more 

 than sixty square miles in extent, the remains of a much larger 

 surface, now lost or destroyed by marine action wearing away the 

 coastline. Red Crag, with flints and phosphates, occurs a few miles 

 inland as far as Sudbury and Monks Eleigh. 



The fossils belong to two series, the older one rich in fishes and 

 crustaceans, usually embedded in a highly phosphatized clay, the 

 so-called " Coprolites". Amongst the fishes, the genera Cymhiiim 

 and Halecopsis, with the bodies hardly compressed or altered in 

 shape, are very common ; the pavement-toothed Phyllodiis and 

 Pycnodus were frequently obtained when the pits were being worked. 

 The Crustacea have yielded eighteen or twenty species, including 

 one Nephrojjs Reedii, Carter, which has not been recognized elsewhere 

 in the London district. These indicate a zone corresponding 

 generally to that of the London Clay of Sheppey in Kent. Both 

 fislies and crustaceans are often in fine preservation, unlike the 

 shells, which seem to have been absorbed or converted into phosphate 

 pseudomorphs, and are not pyritized as they are in the Sheppey area. 



Casts of a few of the aragonite mollusca are preserved as a sandy 

 or clayey matrix, but slightly phosphatized, the shelly material 

 having entirely disappeared. It is difficult in these cases to 

 determine to which horizon they belong, as the genera Cytherea, 

 Pectunculus, etc., are common to both Eocene and Oligocene, the 

 more so as several species, including Cancellaria {BonelUtia) evulsa, 

 a few Volutes, and Pleurotoma, Rimella and Hippochrenes, pass 

 upwards. Professor Prestwich,^ moreover, says: "The Argile de 

 Boom" (to which I shall presently refer) " attains around Antwerp 

 a thickness of 200 feet, resembling very closely, in its general 

 composition and the facies of its fauna, the London Clay, to which 

 it was originally referred." ^ 



The fauna of these older Eocene clays in England and that of the 

 next group to be considered have very little in common, the 

 teleostean fishes and others just mentioned having passed away. 



^ Geology, vol. ii, p. 382, 1888. 



