284 Reports and Proceedings — Geological Societij of London. 



oxidized the sulphides, caves being formed into which the insoluble 

 ores were carried by the water. Finally, the brecciated mass was 

 recemented. Some foreign material has been introduced, but the bulk 

 of the contents of the pipe is of local origin and consequently not 

 rounded by transport. In other words, the Lahat pipe is a lode 

 deposit which has been converted into a detrital deposit in situ. 



3. "On the Sculptures of the Chalk Downs in Kent, Surrey, and 

 Sussex." By George Clinch, F.Gr.S., F.S.A. Scot. 



The author classifies the various forms of sculpture of the Chalk 

 Downs under three heads, namely, (1) dry valleys of simple form, 

 (2) dry valleys of complex form, and (3) wet valleys. He draws 

 attention to the relatively small catchment areas of the dry valleys, 

 and to the large number of tributary valleys found in some districts, 

 two points which he considers have not received hitherto entirely 

 satisfactory explanation. 



While accepting the view that frozen conditions in former times 

 altered the drainage system of the Chalk, he argues that the most 

 potent excavating force was the frost itself acting on Chalk saturated 

 or highly charged with water. He propounds a theory to account 

 for (1) the great size and breadth of the valleys in relation to their 

 catchment basins ; (2) the ramifications of some of the valley systems ; 

 and (3) the remarkable fact that many dry valleys die out just before 

 the crest of the Chalk Downs is reached. 



April 28, 1909.— Professor W. J. Sollas, LL.D., Sc.D., F.R.S., 

 President, and afterwards Professor W. W. Watts, Sc.D., F.R.S., 

 Vice-President, in the Chair. 



The following communications were read : — 



1. "The Boulders of the Cambridge Drift." By Robert Heron 

 Eastall, M.A.., F.Gr.S., and J. Romanes, B.A. 



For several years past a large number of boulders have been 

 collected from the glacial drifts of Cambridgeshire, and from the post- 

 glacial gravels which have been derived from the drifts. These 

 specimens have been classified geographically and then subjected to 

 a careful petrological examination, with a view to the determination 

 of their origin. Some special collections from Hitchin and Bedford 

 have also been included for comparison. Rocks of Scandinavian 

 origin, and especially those of the Christiania province, are abundant 

 throughout the whole area: such well-known types as rhomb-porphyry 

 and nordmarkite are common. Rocks from the Cheviots and Central 

 Scotland are more abundant than was formerly believed, and specimens 

 have also been identified from the Old Red Sandstone conglomerates 

 of Forfarshire and from Buchan Ness, Aberdeenshire. Lake District 

 rocks probably also occur in small quantity. Much of the Chalk and 

 flints appear to be of northern origin. It is concluded that an older 

 Boulder-clay, containing foreign erratics, the equivalent of the Cromer 

 Till, once extended over the whole district, but was subsequently 

 incorporated with the Great Chalky Boulder-clay. The Scandinavian 

 ice advanced from the direction of the Wash, bringing with it Red 

 Chalk and bored Gryphseas from the bed of the North Sea, and 

 carrying them as far west as Bedford. Rocks from the north of the 



