Speight. — Changes in Terminal Face of Franz Joseph Glacier. 57 



An interesting point to consider is the possibility of periodicity in 

 advance and retreat. My first experience of the glacier was in the year 

 1905, when it was advancing. It was also advancing in 1909 when Bell 

 made his observations, and was retreating in 1912. I cannot determine 

 the precise year when this retreat commenced, but it had probably set in 

 during 1910, and has continued since that date, so that it has been falling 

 back for approximately eleven years. One cannot predict at present v*dien 

 this retreat will end, or what the total length of the cycle is likely to be. 



There are one or two other points to which brief allusion may be made. 

 First, the angle of the shear-planes near the present terminal face, especially 

 those near the eastern front of the glacier, suggests that a great thickness 

 of ice, probably to be measured in hundreds of feet, exists behind the rock 

 bar which stretches from the western wall of the valley towards the present 

 mouth of the Waiho between Barron Rock and peg No. 7. If, therefore, 

 the glacier should retreat farther, the lake along its face will probably increase 

 in size, and it will furnish a suggestion of what usually happens as the ice 

 retreats from a rock bar across a valley. Such conditions must have 

 occurred in the Rakaia, Wilberforce, and Waimakariri Valleys when the 

 ice commenced to retreat towards the heads of the valleys from the barrier 

 near the plains in late Pleistocene times. 



An examination of the rock-surface recently exposed does not suggest 

 that glaciers have any marked power of erosion near their ends even when 

 advancing, slight abrasion being all that was noted on the roches moutonnees 

 recently exposed before the terminal face ; but, of course, this does not 

 negative their power to erode their beds where the ice is thicker. 



The presence of an apparent wave of high ice might have been credited 

 to the influence of an irregular bottom during a period of ice-decline, 

 analogous to the effect of obstructions in the bed of a river, masked as they 

 frequently are at high water, were there not definite proof that ice is 

 actually rising relative to the rocks at the side. In any case, the thickness 

 of the ice is very great even in times of lower level ; all the same, there is 

 some suggestion in the alternating stretches of ice-fall with more gently 

 inclined surface, shown not only in this glacier but in the Fox as well, that 

 if the ice were removed the valley-floor would exhibit in a perfect form the 

 characteristic stairway developed in glaciated regions — as, for example, 

 those in Deep Cove and other valleys at the heads of the sounds of the west 

 coast of Otago. 



In conclusion, I have to express my indebtedness to Mr. Graham for 

 much valuable information and for ready help. He has promised to continue 

 observations and to take photographs of the face from already-selected 

 positions on Park Rock at the same time each year, so that changes in the 

 character and position of the terminal face can be accurately recorded. 

 It is important that they be taken during the same month of the year, so as 

 to eliminate any error due to variation between the summer and winter 

 heat. 



