214 PROCEEDINGS OF THE ACADEMY OF | [March, 



Illecillewaet Glacier. 



The very small recession in the tongue of the Illecillewaet 

 Glacier during the summer of 1899 was found to have been largely 

 made up in 1900, so that the average of the two years was not far 

 from that of the past thirteen, as previously noted/ A distinct 

 shrinkage was observed in all dimensions, but this was most notice- 

 able at the tongue which was now 140 feet above the rock " C," 

 nearly twice the distance of the previous year. 



Our work the past summer consisted : (a) in taking the test pic- 

 ture of the lower part of the glacier, which was made under unfav- 

 orable conditions on August 7, 1900; (b) location of the border 

 of the ice on the map of 1899, and (c) location and measurement 

 of motion of line of plates across the glacier. 



a. Of the test picture nothing need be added except that the 

 series is now complete for three consecutive years and furnishes 

 a most interesting illustration of the comparatively slight and yet 

 none the less constant changes in the contour of the ice. 



b. The position of the edge of the ice was easily located with 

 reference to the several fixed rocks laid out on the general survey 

 of 1899. The plotting of this border line showed that the glacier 

 had receded an average of not far from twenty feet on the sides 

 and sixty-four feet on the extreme tongue. At one point the ice 

 seemed to have changed but little since last year, while at others 

 the recession was more than 100 feet. This constant yearly reces- 

 sion has been proved to be in progress at least since 1887. 



c. The location and measurement of the line of eight plates 

 across the glacier, which were first laid out on July 31, 1899, and 

 had consequently been on the ice almost exactly one year, was 

 taken up on the 6th of August, 1900, on which date plates Nos. 

 1, 2, 3, 4, 5, 6 and 7 were located. Plate No. 8 could not be 

 found, and it was not discovered till several days later, when its 

 position also was obtained. 



All the plates seem to have moved in lines almost parallel with 

 the centre line of the glacier. The following table shows the 

 motion of the plates for the year, and also repeats for comparison 

 the motions determined in the fall of 1899, after the plates had 

 been on the ice but thirty-six days. It will be noted that the con- 



^ P)'oceedmgs of the Academy of Natural Sciences of Philadelphia, 1899» 

 p. 124. 



