Correspondence — Mr. Cecil Carus- Wilson. 429 



district. The principal measurements of the glacier as given by 

 Professor Eeid's survey are a length of 35 miles, a width varying 

 from 6 to 10 miles and an area of 350 square miles. The thickness 

 is 900 feet at the seaward end, and is much less than had been 

 stated. The glacier slopes upward at 1° 15' towards the neve 

 fields; the mountains around the glacier are from 5,000 to 7,000 ft. 

 in height. The glacier is now receding very rapidly, and has 

 retreated 1,000 yards in four years, a rate which far surpasses that 

 ever attained by the Eosenlaui Glacier; its greatest extent was 

 reached about 150-200 years ago. Around the fiord there is plenty 

 of evidence of submerged forests, and Professor Reid therefore 

 suggests that the diminution in the ice has been due to subsidence. 

 The ablation is at the rate of 2 ins, a day, a measurement of much 

 interest as reliable estimates for the Alaskan glaciers have been so 

 far wanting. One of the most important parts of Professor Eeid's 

 work was his measurement of the rate of motion ; this was calculated 

 by Professor Wright at 70 ft, a day. Professor Eeid's careful 

 observations, however, show that this was enormously exaggerated, 

 and that the very highest speed is 7 ft, 2 ins, a day. In a line across 

 the glacier, a little above its mouth, the average daily motion was as 

 follows: 4 ins., 21ft., 5f ft.. Gift,, 4 ft. Sins., 6 ft. lin., 7 ft. 1 in., 

 7 ft, 2 ins,, 6 ft, 2 ins., 4 ft. 9 ins., and 7 ins. The estimate of the 

 amount of erosion that the glacier effects on its rock bed is also of 

 interest. Professor Eeid estimates that it amounts to as much as 

 three-quarters of an inch per annum. The paper is illustrated by a 

 series of photographs, which, though many of them are greatly 

 over exposed, admirably depict the principal features of the greatest 

 of the glaciers on the American mainland. J. W. G. 



coI^I^Es:poI^^IDE^5^o:E3- 



SHAPES OF SAND GRAINS. FLEXIBLE SANDSTONE. 



Sir, — Mr. T. Mellard Eeade in his interesting article on " Glacial 

 Geology," in the July Number of the Geological Magazine refers 

 — page 314 — to the evidence aiforded by the shapes of sand-grains 

 in enabling us to determine the marine or fresh-water character of 

 the deposit of which they form a part. As I have devoted many 

 years to the study of Sands, perhaps I may be permitted to make a 

 few remarks upon the subject. 



Like Mr. Mellard Eeade, I have examined Sands from many parts 

 of the world, and I can endorse his views respecting the (generally) 

 more-rounded appearance of marine sands than river-borne sands. 

 I have found, however, that nearly all river-borne sands have a large 

 pei'centage of cylindrical and tabular grains, while in wave-borne 

 sands (remote from rivers) the percentage of such grains is very 

 small, I have frequently explained what I believe to be the cause 

 of this, and thence the value of the fact in enabling one to distin- 

 guish between those sands deposited by rivers, and those deposited 

 by waves. 



