424 SECTIONAL TRANSACTIONS.— C. 



of Worcestershire. In either case we are dealing with a mountain chain, or 

 ridge, that to begin with separated a high plateau from a low plain. Until 

 deposition overtook erosion the main tendency was for the low plain to 

 extend ever farther into the mountain territory. What remained of the 

 hard core rocks of the mountain functioned meanwhile as a bulwark, pro- 

 tecting the high plateau from encroachment of the plain. Then came 

 deposition, building up the low plain in relation to the high plateau. Thus 

 the original contrast of level on the two sides of the mountain was eventually 

 replaced by a contrast of material. 



Mr. J. F. KiRKALDY. — The constituents of the pebble beds of the Lower 

 Cretaceous rocks of England and the light they throw on the palao- 

 geography of the time (10.45). 



This communication is an interim report of an investigation of the 

 constituents of the pebbly horizons in the Lower Cretaceous beds of South 

 England. More precise evidence than hitherto available, as to the nature 

 of the rocks then undergoing denudation and the directions of the supply 

 of detritus, is accumulating. 



In the Wealden beds of Dorset there is a highly distinctive suite of pebbles 

 indicating the erosion of the metamorphic aureole of the Dartmoor Granite. 

 This suite, except for one or two doubtful pebbles, has not been found in the 

 Weald. The resemblance between the pebbles from the north-west Weald, 

 which are being examined by Dr. Wells and Mr. Gossling, and those from 

 the Lower Cretaceous sands of Bedfordshire, Oxfordshire, Berkshire and 

 Wiltshire indicates in part, at least, a common derivation from the London 

 Platform. In this connection the distribution of the pebbles of silicified 

 oolitic and dolomitic limestone is particularly significant. In east Kent, 

 however, the pebble suite is of a somewhat different character. 



The many interesting types of pebbles found are described and inferences 

 made as to their place of origin. 



Dr. S. M. K. Henderson. — The Dalradian Succession of the Southern 

 Highlands (ii.o). 



A brief account of the results of the study of current and graded bedding 

 in the Leny Grits, Aberfoyle Slates and Ben Ledi Grits. These three 

 groups have generally been adopted as the youngest members of the Perth- 

 shire Succession, and were included thus by Dr. Bailey in his Iltay Nappe. 



From Loch Lubnaig in the north-east to Loch Lomond in the south-west 

 (Geological Survey, Sheet 38) current and graded bedding has always given 

 the same evidence. The generalised dip is 60° to the north-west. 



The evidence shows that the Leny Grits to the south-east of the Aber- 

 foyle Slates are upside down, and are younger than the latter, which they 

 underlie. On the north-west side, the Ben Ledi Grits are also younger 

 than the Aberfoyle Slates which they superimpose. 



On lithological grounds it seems reasonable to correlate the Leny and Ben 

 Ledi Grits as one formation younger than the Aberfoyle Slates, the former 

 being the imder limb, and the latter the upper limb of a steeply overturned 

 anticline. This would then be a structure comparable to the Carrick 

 Castle Fold, an anticline closing to the south-east, in the Iltay Nappe of 

 Bailey. The series of dislocations between the Leny Grits and the Highland. 

 Border Rocks may, upon further investigation, prove to be the base of this 

 large overfold of Dalradian rocks. 



