Yol. 65.] THE BOULDERS OP THE CAMBRIDGE DRIFT. 263 



travelled roughly south-south-eastwards ; and we must remember 

 that, several years ago, Mr. Rowe had mentioned a similar mixture 

 of these rocks near Pelsted in Essex, a place well east of Cambridge 

 and a little south of Hitchin. In like manner, as was already 

 known, erratics from Shap Fell had crossed the same stream of 

 boulders from the north, but in the contrary direction ; and the 

 Arenig dispersion also traversed from west to east those from the 

 Lake District and Southern Scotland. These facts were very 

 difficult to explain on any hypothesis ; and he would only say 

 that, in seeking to do this, we must remember that, in the Glacial 

 Epoch, the ice in the Scandinavian and the British areas would be 

 likely to advance and retreat simultaneously. The paper, in short, 

 was a very important one, and, as he well knew, had cost the 

 Authors much time and trouble. 



The Rev. E. Hill welcomed the paper as a most important 

 addition to Glacial Geology. His own few observations fully agreed 

 with the Authors' descriptions. The only point that he was inclined 

 to question was the entrance of the boulders by way of the Wash. 

 The Great Chalky Boulder-Clay seemed to have come from the west 

 of the Lincolnshire Wolds into Norfolk and Suffolk, but to have 

 found no exit by the Wash. The Yorkshire Clays which were 

 continued east of the Lincolnshire Wolds, into the Cromer Till, 

 seemed to have found no inlet by the Wash. If the Clays did not 

 take this course, was it likely that the boulders should ? 



Mr. Lamplugh remarked that the Authors' observations were 

 consonant with the general evidence of the East British drifts in 

 showing that the glaciation of this region was effected by an ice- 

 sheet spreading from the basin of the North Sea. This basin 

 appeared to have been itself the main centre of ice-accumulation, and 

 the contribution from the glaciers of Scandinavia probably formed 

 only a subordinate part of the mass. Boulders had been dispersed 

 over the sea- bottom before the advent of the land-ice by which they 

 were again transported, so that it was not always safe to postulate 

 a direct line of travel for them. The geology of the floor of the 

 basin also must be borne in mind in considering the sources of 

 the boulders. The distribution of the North British rocks discussed 

 by the Authors implied that the basin was continuously blocked with 

 the East British ice-sheet until a late stage, and afforded no support 

 to the idea of separate glaciations mentioned by the President. 



Dr. A. E. Salter called attention to the remarkably rounded 

 character of the small boulders of rhomb-porphyry exhibited, and 

 stated that he had found pieces of this rock farther west at Grove- 

 bury near Leighton Buzzard, and near the crest of the Chalk 

 escarpment at Great Offley (500 feet above Ordnance-Datum), 

 between Hitchin and Luton. Quite recently, Mr. G. Rotter had 

 found a rounded boulder, similar to those exhibited, as far south 

 as Eortis Green, Highgate, at 300 feet above Ordnance-Datum in 

 Chalky Boulder-Clay. 



The Secretary read the following notes which had been 



