Fowler. — Ice -striated Rock-surface at Circle Cove. 175 



Art. XIX. — On an Ice-striated Rock-surface on the Shore of Circle 



Cove, Lake Manapouri. 



By J. M. Fowler. 

 Communicated by Professor J. Park. 



[Bead before the Otago Institute, 9th November, 1920 , received by Editor, 31st December, 



1920 ; issued separately, 4th July, 1921.] 



Plate XXXVII. 



On the 16th May, 1919, in the stratification of a series of low-lying bush- 

 clad hills known as " The Peninsula," Mr. Guy Murrell and the writer 

 discovered a series of rounded, though fairly flat, rocks on the shore of 

 Circle Cove, which is the first little inlet to the left after rounding Stony 

 Point. On these rocks were marks quite different from anything that 

 could be attributed to jointing or fracturing, and which there was no diffi- 

 culty in attributing to ice-action. The marks run parallel for the length 

 of the rock-exposure, and follow all the undulations. In places they are 

 lost from view, as the hollows between the exposed parts either dip below 

 water-level or are filled with gravel which has drifted into them. 



The striated shelf extends along the shore about 150 yards, and is 

 about 20 yards in width, at the summer level of the lake. 



The marks are of all sizes, from sharply cut narrow lines to a trough 

 about 2 ft. deep and 30 ft. or 40 ft. long, the bottom of which is polished 

 as smooth as glass. The freshness of the marks is very noticeable. 



The rocks as seen on the shore consist of beds of conglomerate, sand- 

 stone, fine silt, and thin seams of lignite. The conglomerate consists of 

 granitic boulders set in a matrix of exactly the same material, so that 

 when freshly broken it looks like homogeneous rock, but where weathered 

 its components show out. The ice-marked shelf seems to be simply the 

 lower stratum of the shore-rock, from which the overlying beds have been 

 eroded. The scratches are sometimes in the conglomerate and sometimes 

 on the other strata, according as the contour rises or falls. All, however, 

 are polished so smooth that it is only where a face appears that the 

 different layers can be distinguished. 



