508 ■ PROCEEDINGS OF THE ACADEMY OF [1899, 



was about 40°, and as the reference point was located at the level 

 of the ground moraine below, the vertical height of the plate and the 

 diagonal distance were noted, from which the horizontal motion 

 was calculated. The vertical distance from the ground moraine 

 was obtained through a crevasse near by, while the direct distance 

 from the marked boulder was readily measured with the tape line. 

 Unfortunately, after these measurements had been made for sev- 

 eral days, and very satisfactory results obtained, a great mass of 

 the tongue on which the plate had been located broke away fi'om 

 the main glacier. Immediately the daily rate of flow changed 

 from a little over five inches to a fraction under three, and 

 remained almost constant. Whether this apparent motion was due 

 to the melting of the plate in the ice, or to the reduced flow of 

 the smaller mass when not urged on by the parent glacier, was not 

 determined. The crevasses seemed to widen from day to day in 

 spite of the fact that the motion of the ice alone would cause them 

 to become narrower. 



Table of Motion of Plate No. 9, on Tongue of Illecelleicaet Glacier, Brit- 

 ish Columbia, August 1st to 20th, 1S99. 



a. Number of Observation. 



b. Date of Observation 



1 

 8/1 



2 



8/2 



3 



8/6 



4 5 



8/15 8/20 



c. Interval since last measurement (days). \ 1.24 



d. Actual horizontal motion of plate (ins. ) 



e. Motion of plate per day (inches) 



2. Measurement of recession and other changes since 1898. 

 After the rapid changes of the last few years we were surprised 

 that very little alteration had taken place in the form of the 

 glacier since last summer. In the fall of 1898 the average c^ai/y 

 recession was nearly eight and one-tenth inches, while the average 

 annual recession was fifty-six feet.* Measurements showed that 

 on July 29th, 1899, the tongue was seventy-one feet above the 

 marked rock " C," (see map, Plate XX) and on August 20th, 

 seventy-six feet. These indicate a recession of but sixteen feet 



•Froc. Acad. Nat. Sci. Phila., 1899, pp. 123. 124. 



