REVIEWS 205 



glaciers during a period of recession and overridden wlien the ice 

 readvanced. Some important modifications of this general history are 

 suggested. 



Among the many interesting results reported, are observations on 

 variations in the extension of Muir glacier between 1880 and 1892. 

 Records of the position of the extremity of the glacier in 1880,. 

 1886, and 1890, showed an apparently continuous recession of about 

 250 yards a year, but in 1892 the ice front had advanced on an average 

 of approximately 300 yards beyond its position in 1S90. The most 

 marked advance was in the central portion where the ice current is 

 known to be most rapid. In a footnote it is stated that photographs 

 taken in 1894, show a recession to the position occupied in 1890. 



The rate of flow of the ice near the end of Muir glacier, as meas- 

 ured bv G. Frederick Wright in 1886, and by Reid in 1890, showed 

 great discrepancies which could not be reconciled. This question 

 which has led to some discussion during the past five years, is briefly 

 considered and the accuracy of the measurements made in 1890 main- 

 tained. It will be remembered that the maximum rate of flow in the 

 central portion of the glacier near its terminus, was stated in the report 

 of the expedition of 1890 to be about seven feet per day. 



A map of the end of Girdle glacier on a scale of 500 feet to an 

 inch, shows the manner in which it thrusts its extremity into the side 

 of Muir glacier, to which it is tributary, so as to cause the lateral 

 moraines on the main glacier to curve about it in rude semicircles. 

 Stakes were placed along the margin of the expanded terminus of 

 Girdle glacier and their direction and rate of movement measured 

 twenty-four days later. The rate of motion varied from 1.8 to 2.6 

 inches per day ; the direction of movement revealed a spreading of 

 the ice of Girdle glacier, and a slow movement in common with the 

 general flow of Muir glacier. Other instructive facts concerning the 

 unique phenomena revealed by Girdle glacier are recorded. The 

 stakes placed in the ice melted out, but their positions were preserved 

 by placing three small iron plates about each one. The plates, as is 

 the rule with small dark objects lying on the ice, sank into it as melt- 

 ing progressed, and thus maintained their position. 



Peculiar holes in the surface of Muir glacier, from a few inches to 

 six or eight feet deep, with a diameter of six to eighteen inches, were 

 found to be due to the lowering of the surface by melting, so as to 

 expose cavities that previously existed in the ice. The holes within 



