SECTIONAL TRANSACTIONS.— C. 321 



(b) Upper Diluvium, which rests unconformably on the outcrops of the 

 disturbed deposits. 

 To the south, near Sassnitz, the general strike of the disturbed chalk is NNW-SSE, 

 and there is a general dip of the beds approximately to the south, in the coast 

 sections. 



Traced from north to south the structure may be divided into three zones : — 



(1) A 'horst' of chalk to the north forming the lofty cliffs of Stubbenkam- 



mer, bent into a magnificent sigmoid curve at the Konigsstuhl bluff. 



(2) A zone of thrust planes, in the central area between Sassnitz and Kolicker 



Ufer, a distance of three miles. In this zone the Lower Diluvium is 

 repeatedly intercalated in the chalk. 



In each case the lower boulder clay rests evenly on the underlying inclined face 

 of the chalk, while a thrust plane is associated with the ' hanging wall ' of the 

 overlying chalk, the ' sole ' of the thrust transgressing the tripartite succession of the 

 drift, disturbing and, in places, removing either the whole or portions of the upper 

 members. The chalk, between adjacent thrust planes, always assumes the forni of 

 a truncated flow-curve or squeezed anticline. All observers agi-ee that the lower 

 boulder clay consists of isolated strips severed from a once continuous sheet ; it is 

 therefore a valuable datum-line. This zone proves, in a convincing manner, imbricate 

 or ' schuppenstruktur,' due to ice-action, repetition occurring at least fourteen 

 times. 



(3) The third zone occurs near Sassnitz and is characterised by a peculiar de- 



velopment of 'false-domes,' and ' pseudo-synclines ' or drift-lined hollows 

 in the chalk, associated with thrust. 



The structure is analogous to that of the Moen area south of the Sommerspir, 

 described at the Oxford Meeting last year. 



The cost of this investigation was defrayed by a grant from the Sladen Trustees, 

 1926, for which I express my thanks. 



Dr. G. Slater. — The Structure of the Mud Buttes and Tit Hills of Alberta. 

 Canada. 



Examination by 0. B. Hopkins of the district in question showed Cretaceous beds 

 surrounding the buttes and hills dipping gently southward, while. in the Mud Buttes 

 the sediments, disposed irregularly in miniature folds, prevailingly dip about 30° N.E. 

 The anomalous structure was tentatively explained by Mr. Hopkins as due to pressure 

 of an advancing ice-sheet against an obstructing outcrop which was moved en masse 

 with consequent thrusting and folding. 



Studies by the writer in 1924 confirm the essential point of Hopkins' view — namely, 

 that the Mud Buttes and Tit Hills owe their origin to ice-action ; but the detailed 

 relations observed in the field and described in this paper show that these interesting 

 local topographical features are built up by accretions in the form of comparatively 

 thin lenticles of englacial material, the origin being similar to that of deposits 

 investigated at several European localities. 



Structurally the Mud Buttes present, from south to north, three zones : (1) bluffs 

 with little compression and no overfolds, this zone being analogous to a ' horst ' ; 

 (2) a zone of compression ; (3) overfolds forming the highest part of the hills. The 

 structure was built up from south to north, but movement of the beds was in the 

 reverse direction. 



The moulding of material forming the southern bluffs has been from below upwards. 

 The material is composite in character and has been moved as individual ledges or 

 lenticles along thrust planes. Against the sigmoid curve and associated thrust plane 

 on the exposed side of the bluffs, which acted as a ' horst,' the central zone of compressed 

 material has been squeezed, resulting in the formation of folds, and rippling. The 

 upper surface of the central zone finally formed a glide plane for the passage of other 

 material forming zone 3. This material moved in the form of overfolds dissected by 

 thrust planes, the whole having a radiating structure. The exposed or northern 

 flank formed one of the major thrust planes of the area. Although the axes have a 

 general east-west trend, there is a slight southerly deflection on the eastern flank. 



1927 Y 



