338 Ti-ansactiojis. 



Canterbury which has been subject to glaciation m the past, or where 

 glaciers occur now. The conclusions I have come to were made quite 

 independently, and this may perhaps lend additional weight to them, a& 

 they are the result of observations in a country far distant from that where 

 Professor Hobbs made his. Professor W. M. Davis, of Harvard University, 

 has lately informed me in a letter that Matthes was the first to point out 

 the relation of corrie glaciers to saddles and passes, in a report on the 

 glaciation of the Big Horn Mountains (United States Geol. Survey, 21st 

 Annual Report, 1899-1900). 



(h.) Glacier Potholes. 

 (Plate VI, fig. 2.) 



A very interesting and suggestive landscape-form occurs at the j mic- 

 tion of the Lake Stream with the Rakaia. This is a romid hollow over 

 300 ft. deep and about half a mile across, with the whole interior cut into 

 horizontal or nearly horizontal shelves. These have evidently been produced 

 by the erosion of ice moving in an approximately circular direction in 

 horizontal planes. There is a remarkable resemblance to a pothole in an 

 ordinary river, and the occurrence serves to emphasize the close resemblance 

 that exists under certain circumstances between the erosion of a river and 

 that of a glacier. 



If the similarity in the action of the two streams 'be grarited, the ex- 

 planation of the formation of the hollow is quite easy. A portion of the 

 great Rakaia Glacier running from w^est to east turned south just above 

 the Lake Stream, rounded the spur at Prospect Hill, and turned up the 

 valley towards Lake Heron. The ice impmged against the massive hill to 

 the east of that valley, and just at the jimction an eddy was formed which 

 scoured out the hole, the horizontal terraces being a result of that gyratory 

 motion. AVhen the ice disappeared a rock-bomid lake occupied the hole, 

 which has since been emptied through the degradation of the barrier by 

 the outflowing stream. An exactly analogous case occurs at the junction 

 of the Cass River with the Waimakariri. The Waimakariri Glacier at the 

 time of its greatest power flowed from west to east, and on reaching 

 Goldeney's Saddle, about six miles below the Bealey, overrode the end of 

 the spur and turned south-east into the valley towards Lake Pearson and 

 the head of Sloven's Creek, following the line of the Midland Railway. On 

 the east side of Goldeney's Saddle it formed a rock-bound basin exactly 

 similar to the one in the Rakaia, but not quite so perfect. The Cass River 

 now rmis through it, and passes through a notch in the rim towards the 

 Waimakariri. The whole locality presents a remarkable resemblance to 

 that of the Rakaia. Goldeney's Saddle and its semi-detached knob corre- 

 sponds exactly to Prospect Hill. There is a momitain mass on the east side 

 of the inflowing stream, against which a part of a great glacier impinged. 

 The rock-bound and ice-scoured pool with horizontal terraces lies between 

 the two, no doubt in both eases formmg a lake on the retreat of the ice, and 

 then this has been emptied in both cases by the erosive action of a stream 

 coming in from the south. Both occurrences emphasize the erosive action 

 of the ice under similar conditions, and its capacity to scour out rock- 

 bound basins in circumstances such as would favour the formation of eddies 

 if water and not ice were the moving element. This action explains the 

 formation of many of the rock-bomid ponds and small lakes which occur 

 freely in comitries which have been glaciated. Numerous instances of 



