320 SECTIONAL TRANSACTIONS.— C. 



a great thickness of beds extending from North Yorkshire down to Pendle Hill, but are 

 apparently absent farther south. The second such invasion was that of the 

 Kinderscout Grit and associated beds, which are of great thickness in Derbyshire, and 

 dwindle away northwards to a few feet near Clapham. Of less importance and not so 

 clearly defined is the invasion represented by the Third Grit of Lancashire, which has 

 a maximum in the west of Lancashire. Lastly, we have the Rough Rock extending 

 in one unbroken sheet perhaps over the entire Midland Province, and in its regular 

 character showing a marked contrast to the preceding great lenticular masses of grit. 



Mr. E. G. Hudson. — A Mid-Avonian Unconformity in the Craven Lowlands. 



Afternoon. 

 Excursion to Bell Busk and Skipton. 



Friday, September 2. 



Prof. P. G. H. Boswell. — The Cleavage-Fan in the Ludlow Rocks of the 

 Denbighshire Moors and Clwydian Range. 



One of the most interesting tectonic features found by Mr. Howel Williams during 

 his investigation of the Snowdon district of North Wales was the presence of a ' cleavage- 

 fan.' A similar fan has been traced in the area of Ludlow rocks forming the 

 Denbighshire Moors and the Clwydian Range (which is separated from the Moors by 

 the down-faulted area of the Vale of Clwyd). 



The strike of the cleavage is approximately east-west ; in the moorland area it 

 strikes frequently north of east, and in the Clwydian Range it often swings to north of 

 west. Where hard sandstone bands intervene in the muddy Salopian sediments, or 

 where the rocks are disturbed by post-Caledonian faulting, the cleavage-direction 

 varies considerably and may, for the purpose of this discussion, be regarded as 

 anomalous. 



In the northern part of the Moors, behind Abergele and Colwyn Bay, the cleavage 

 displays a southerly dip at angles increasing from 45° to 80° as we proceed south- 

 wards. Along an east-west belt through Llanefydd, Llanfair-Talhaiarn, and Pentre- 

 Llangerniew, the cleavage becomes vertical or oscillates rapidly, dipping towards the 

 north or south at angles greater than 80°. South of this area, over the greater part 

 of the Moors, the cleavage-planes dip steadily northwards at angles varying from 

 40° to 80°. 



In the northern part of the Clwydian Range the cleavage is southward-dipping. 

 Over the central part it is vertical or rapidly oscillating, and in the southern part 

 it is consistently northward-dipping. 



The formation of the fan is attributed to deep-seated movements due to pressure 

 acting from the directions of the northern and southern margins of the geosyncline of 

 Ludlow rocks, and directed towards the centre. 



The middle or ' axis ' of the cleavage-fan is in places translated by post-Caledonian 

 faulting. Displacement by tear-faulting, as distinct from vertical movement along 

 the fractures, may thus be determined. 



Dr. G. Slater. — The Structure of the Disturbed Chalk and Diluvium on the 

 East Coast of the Isle of Riigen (Jasmund District), Germany. 



The classical disturbances on the east coast of the Isle of Riigen (Jasmund District) 

 extend from Sassnitz to Stubbenkammer, a distance of five miles. The cliffs are 

 composed of chalk associated with drift. The former belongs to the Upper Senonian 

 Pencil Chalk and is unstratified, the bedding being indicated by flint-bands. A 

 representative fauna was collected from the Sassnitz pits and confirms the opinion of 

 previous workers that this zone is equivalent to the Trimingham horizon of England. 

 Macroscopic fossils in the cliffs, however, are scarce. The drift belongs to two 

 6eries : — 



(a) Lower Diluvium, associated with the disturbed chalk. This drift is 

 tripartite, two boulder clays being intercalated with stratified sands of 

 fluviatile and fresh-water origin. 



