338 ifR. F. W. HAEMER ON THE tENHAM BEDS [Aug. 1 898, 



(No. 12), and the third from the seam of bright blue stuff brought 

 from the bottom of the boring at the same place. 



There is no evidence to show that the Coralline Crag extends 

 either -west or east of the main mass of the formation exposed 

 between the rivers Deben and Aide. The Red Crag rests against 

 it, however, on the west side in the parishes of Chillesford and 

 Iken, on the east side near Orford Castle, and at pits 19 & 20 at 

 Sudbourne. Mr. ^\^hitaker states,^ moreover, that White Crag, con- 

 sidered by him as of Eed Crag age, was met with in borings at the 

 Lantern marshes at Orford, resting on the London Clay at a depth 

 of about 30 feet, no Coralline Crag being there present. 



Having established the fact of the progressive dip of the 

 junction between the Coralline Crag and the London Clay between 

 Sutton and Sudbourne, and having failed to discover in the beds 

 penetrated any evidence of the continuity of the supposed zones in 

 the outliers at the former localit}', it did not seem necessary to 

 carry the borings farther north, especially in view of the increasing 

 di£B.culty and expense of doing so. As, however, the gradient is 

 more or less uniform where it can be tested, it does not seem 

 improbable that the line separating the two deposits, which can be 

 drawn with accuracy from Sutton to Sudbourne, may be produced 

 towards Aldeburgh and SizeweU also (see fig. 5, p. 328). If this 

 be so, the base of the Crag would be reached at a depth of about 48 

 feet under the former, and of about 68 feet under the latter place, 

 making the total thickness of the formation 60 feet at Aldeburgh, 

 as^t is at Sudbourne. 



"^ the sections (figs. 3, 5, & 7, pp. 324, 328 & 332) I have shown 

 the various positions in which seams of large shells, either perfect or 

 in the form of casts, occur in the unaltered and in the decalcified 

 Crag. I have already stated where they are to be found in the 

 former. In the latter they may be seen at the following, among 

 other localities: — At pit ISTo. 14, near Sudbourne Park gates; at 

 Iken, Nos. 27 & 28 ; at Aldeburgh, No. 29, close to the river-bank ; 

 No. 31, near the railway-station ; and at Nos. 32 & 33, farther 

 north. Some of these seams are chiefly composed of the casts of 

 Cardium decorticatum , while in others Cyprina islandica is the pre- 

 vailing form. The first-named occur in several places in the upper 

 part of the Crag, as at Sudbourne and Aldeburgh, and it might be 

 supposed that they represent a later, as those containing Cyjprina 

 represent an earlier zone. At Iken, however (No, 27), midway 

 between those two localities, both forms are present in the rock- 

 bed, though Cyjprina is by far the most common.^ These species 

 occur in all parts of the Eed Crag, however, and neither of them 

 has any stratigraphical value. In his list of the mollusca of the 

 Coralline Crag, Prestwich remarks of both that they occur passim. 



My son, W.D.Harmer, has taken two photographs of the sections at 

 Iken (No. 27). The first (fig. 9, p. 340) shows a small patch of shelly 



1 Mem. Geol. Surv. 1886, Aldborougb, p. 53. 



^ Mr. Kendall found a bed containing Cardium decorticatum abundantly in the 

 lower part of the Crag at Gomer (see p. 334). 



