36 Professor J. W. Gregory — The English " Eskers ". 



bed is a surface wash, of angular broken flints ; this rests on shell- 

 bearing sands, or on boulder clay, which is sometimes in disturbed 

 patches, but at the southern end of the pit occurs as a sheet 2 feet 

 thick, resting upon an irregularly denuded surface of the sand. The 

 foreign rocks in this boulder clay show that it belongs to the North 

 Sea Drift. The bedded shelly sands were therefore deposited in a 

 depression earlier than the North Sea Drift ; and that the present 

 form of the sand hills is due to denudation later than that Drift is 

 shown by the angular flint gravel which caps them and which was 

 formed as a wash down the sides of the valley. When this gravel 

 was formed a continuous slope must have extended from the Chalk 

 slopes to the summit of the ridge. Some outliers of the sands to 

 the S.W. of the ridge support the conclusion that its form is due to 

 denudation. 



3. The Blakeney Dotvns. — The most esker-like formation which 

 I have seen in East Anglia is that known as the Blakeney Downs, 

 a sinuous bank of sand and gravel wbich lies on the high ground 

 (80-150 feet above O.D.) to the W. and S.W. of Blakeney. Its 

 course has been described by Holmes ^ and H. B. Woodward.^ 

 The structure is clearly shown in a series of extensive sections. 

 The redeposition of some of the material has in places given rise to 

 a dip parallel to the slopes. The most instructive sections are on 

 the S.B. side of the road going S.W. from Blakeney. The surface 

 layer is usually a residual bed, a foot or two thick, composed of 

 closely packed flints. Beneath this layer is false-bedded fluvio- 

 glacial grave] ; this rests on the eroded surface of a lower series 

 of similar gravels and bedded sands. The sides of this pit vshow 

 the longitudinal variations in the deposits ; but in spite of the 

 clear and numerous sections along the ridge I saw no evidence of 

 osar-like cross banding. The sections show that the original bedding 

 of the fluvioglacial beds has been abruptly cut off on the margin 

 by later denudation, and that on this worn surface was deposited 

 a sheet of boulder clay, which, at the N.W. corner of the main pit, 

 rests upon 12 feet of marl formed of redeposited Chalk and belonging 

 to the North Sea Drift. 



Isolated from the main ridge by level tracts of boulder clay are 

 mounds of sands and gravel, such as Joe's Hill. Similar gravels 

 are extensively developed on the opposite side of the River Glaven, 

 E. of Wiverton, where they are shown in large pits. 



The Blakeney " esker " is either part of a wide sheet of fluvio- 

 glacial gravel, or of a kame formed before or during the deposition 

 of the North Sea Drift ; it contains biotite-gneiss and other rocks 

 characteristic of that drift ; bat the boulder clay of that drift rests 

 on an irregular eroded surface of the kame gravels. It may be 

 residual from a widespread sheet of sand and gravel, or a denuded 



1 Geol. Mag., 1883, p. 441. 



2 Mem. Geol. Surv., 68 S.W. and N.W., 1884, pp. 34, 35, 37 ; Geol. Engl, 

 ■and Wales, 1887, p. 510 ; Proc. Norm. Geol. Soc, i, pt. 8, 1884, p. 266. 



