and on the Drift of the Eastern Counties. 199 



structure of the county, be expected ; good sections, however, 

 showing the passage may be found in the pit behind Sizewell 

 Gap already alluded to, in a pit a mile west of Leiston, on the 

 Saxmundham road, and in a pit at Hoo, a mile on the Charsfield 

 side of the bridge over the Deben. Over Suffolk, the upper 

 part of the lower Drift is marked by beds of coarse gravel, the 

 stones being large and angular, and sparsely scattered in the 

 sand : they are unlike the gravels that occasionally, even in this 

 area, occur near the base of the deposit, the latter being more 

 rounded and thicker-bedded, while the former have the character 

 of being ice-borne, and much resemble the small boulders occur- 

 ring in the Drift clay. The characteristic pebble of the lower- 

 Drift beds is a pink quartzite, which I have identified more 

 nearly with a quartzite from Freyburg than with any other. It 

 is probable that the lower-Drift bay, of which only the lower and 

 western border touched England, extended across the north of 

 Europe to a great distance in the direction of Germany, and that 

 the gravels accumulated in it were largely supplied with detritus 

 carried from that country along the southern shore of the bay. 

 The depression that introduced the upper- Drift seems to 

 have been both sudden and uniform ; and if the view be well 

 founded which I have taken as to the formation of the valley- 

 system* of Eastern England — that all the inequalities of surface 

 now exising there are of an origin later than the Drift — we may 

 conceive that a sudden, though moderate, depression would at 

 that time have submerged the very extensive area occupied by 

 the Jurassic, Cretaceous, and Tertiary strata : the materials of 

 these, and particularly the two former, it is well known, have 

 largely contributed to the upper Drift, the supply of which 

 appears to have been chiefly furnished from the British strata. 

 The thickness of this upper Drift over Suffolk and Essex does not, 

 where least denuded, exceed the maximum thickness of the lower 

 Drift ; and its deposition seems to have ceased before the spread- 

 ing of the great erratics of the northern counties commenced. 

 At any rate, the great erratics are generally absent over the 

 southern part of the eastern counties; and as no denudation 

 could well have removed them, but must have allowed them to 

 sink upon the uncovered beds, we may assume that the causes 

 giving rise to the erratic distribution of northern England did 

 not exist over these more southern counties. Probably before 

 the high lands of the northern part of England were submerged, 

 the great plain then formed by the strata newer than the Trias 

 had sunk to a depth beneath the sea too great to arrest icebergs 

 on their transit, if these were the means of spreading the erratics ; 

 on the other hand, the greater distance of these counties from 

 * Phil. Mag. ser. 4. vol. xxvii. p. 180. 



