TRANSACTtOXS OF SECTION C. 



759 



on botli slopes of the watershed through which they are cut, with no approach to 

 base-levelling to the existing streams. They all slope from the west or north-west 

 in an easterly or south-easterly direction, Iheir lower terminations being often 

 marked by level or gently sloping fans of detritus. The altitude of such an 

 alluvial flat corresponds with that of the head of a similar valley on the next spur 

 to tlie south-east. The very temporary nature of the surface levels of the lakes, 

 as attested by the rapidity witii which the gorges were cut, renders the produc- 

 tion of beaches similar to those observable in Glen Eoy and neighbourhood very 

 unlikely. We have not found any but doubtful examples ; the detection of such 

 minor features in a country consisting of nearly horizontal beds of hard sandstone 

 and soft shale must ever be a matter of extreme dilhculty. 



A list was brought forward of over forty overflow-channels with their altitudes, 

 which mark the successive levels of the surface-waters of the lakes. During the 

 maximum glaciation there were six lakes on the south side. Those on the north 

 side were only in existence during retreat. 



The authors desire to thank Mr. P. F. Kendall, F.G.S., for much valuable 

 advice in connection with the extra-glacial drainage systems. 



6. The Source and Distribution of the far-travelled Boulder's of East 

 Yorkshire. By J. W. Stather, F.G.S. 



A-bout ten years ago Mr. G. W. Lamplugh counted and roughly classified the 

 larger boulders of Flamborough Head and other selected localities on the York- 

 shire coast. The work has been continued by the members of the Hull Geological 

 Society, who have eximined and tabulated upwards of 3,500 boulders of 12 inches 

 and upwards in diameter (the size-limit adopted by Mr. Lamplugh). 



But besides the larger boulders attention has been paid to the smaller stones 

 of the drift, which have also yielded results of much interest. 



"With regard to the larger boulders (lists of which have been published in the 

 reports of the Yorkshire Fioulder Committee and of the British Association 

 Committee) it has been sought to discover the proportion of rocks from distant 

 sources, after the elimination of the secondary rocks of local derivation. 



The following table, showing the boulders of two selected localities in the 

 southern part of the Yorkshire coast and two in the northern part, will serve to 

 illustrate the general distribution : — 



The investigation 



shows — (1) The proportion of Carboniferous sandstones and 

 limestones increases northward. (2) The whin-sill increases southward proportion- 

 ately though not numerically, probably bearing transport better than (1). (3) The 

 magnesian limestone in the form of laiye boulders disappears southward. (4) The 

 granites, gneisses, &c., decrease both proportionately and in numbers northward, 

 except the Shap granite and the Cheviot porphyrites, which show a rapid 

 increase in the same direction. A considerable number of (4) agree with well- 

 known rock types of Scandinavia, and these are more plentiful in the south of the 

 county and in Lincolnshire than in North Yorkshire. The unknown rock types 

 included in the same group agree in this respect with these recognisable Scandi- 



