﻿550 S. V. Woocljjun. — American and British Surface- Geology, 



■undergone destruction there by its pressure and motion.^ For several 

 miles round Thetford upon the high ground the Upper Glacial presents 

 a very peculiar condition, as it consists of a gritty sandy kind of 

 raaterial, intermingled in which are often masses of stiff blue morainic 

 clay, which resemble the clay of the Upper Glacial elsewhere, the 

 whole resting upon glaciated chalk. This morainic material, which 

 forms some of the lightest and most barren heath land in England, 

 appears to be moraine formed by the destruction of the Lower and 

 Middle Glacial deposits (and possibly also of some of the earliest 

 deposited Upper Glacial) during the time when the inland-ice was 

 pressing upon the western side of this land-belt ; and it terminates 

 quite abruptly, and gives place to the stiff heavy clay which forms 

 the usual character of the Upper Glacial, just where the Middle 

 Glacial sets in beneath it. The Chalk also beneath it is glaciated, 

 as it usually is on the west of the line to which this land-ice reached. 

 The state of things which thus existed after the earliest part of 

 the Upper Glacial had accumulated appears to me to throw light 

 upon the age of the well-known lacustrine bed two miles from the 

 Eiver Waveney, and situated at Hoxne, on the table-land out of 

 which the valley of this river is excavated. This bed of laminated 

 brick-earth and sand, with freshwater moUusca and PalEeolithic 

 implements, was elaborately described by Mr. Prestwich in the 

 Phil. Trans, for 1860 and 1864:, and shown to occupy a small 

 basin-like hollow in the chalky clay. I examined the locality with 

 Mr. Prestwich's sections some years ago, and could detect no error 

 in them.^ The deposit is so placed that on one side it has been 

 denuded by the excavation of a valley which is lateral and tributary 

 to that of the Waveney, viz. the Goldbrook Yalley. This fact, and 

 the occurrence of some gravels capping the chalky clay along the 

 edges or brows of the main valley, induced Mr. Prestwich to con- 

 tend that the accumulation of the brick-earth and gravels must have 

 preceded the excavation of the Waveney Yalley, because, if not, it 

 would be necessary to infer either that the valley was filled at the 

 time with the sea or by freshwater. The first of these alternatives 

 was rejected for want of any evidence of it, and as being repugnant 

 to the facts affecting the case ; while the latter was evidently a 

 physical impossibility. Hence the view adopted was that the Hoxne 



^ The limit up to which this inland-ice pressed upon and destroj^ed all the pre- 

 ceding glacial deposits is marked, as nearly as can be defined, by a line which, start- 

 ing in Nortb-west Norfolk, a little east of Docking, nms south between Swaifbam 

 and East Dereham, and between Thetford and East Harling, where the ice began to 

 draw in to form the glacier-tongue which passed through the Waveney Valley ; from 

 whence it runs by Bottesdale, south of which the glacier-tongue through the Gipping 

 A'^alley went off. From thence the line runs westwards, and is more difficult of defi- 

 nition. The tongue which passed down the valley of the Wensum and Yare probably 

 went off near the starting-point of this line. 



2 I think it, however, probable that the chalky clay and underlying (Middle 

 Glacial) gravel do not possess the regular horizontality which Mr. Prestwich gives to 

 them ; and also that between them and the chalk some of the Contorted Drift, out of 

 which the valley was first interglacially excavated, may be present. The representa- 

 tion given by Mr. Belt in the Quart. Journ. of Science for 1876 does not ia any 

 respect agree with my view of the facts of the case. 



