PROGRESS OF THE SEASONS. 97 



With regard to the progress of the seasons, the 

 " Indian summer," as it is called, brought us three 

 weeks of fine weather after our arrival in Sep- 

 tember. The centre of Bear Lake usually remains 

 open till late in December, but by the middle of 

 October the bays and straits are frozen across. 

 As the structure of ice has of late years attracted 

 the attention of speculative geologists, principally 

 in connection with the movements of glaciers, I 

 am induced to mention here a few facts which in- 

 truded themselves on my observation during my 

 residences in the fur countries. 



The first step in the freezing of rivers in this 

 rigorous climate, after the water has been cooled 

 down to 32° by a succession of cold weather, is the 

 formation of somewhat circular plates of ice, six or 

 eight inches in diameter. These drift for a time 

 with the current, until they have become numerous 

 enough to cover the surface of the water, when 

 they are arrested in a narrow part of the river, 

 or by any slight obstacle, and speedily adhere to 

 each other, after which the interstices between the 

 circles fill rapidly with crystals that bind all 

 firmly together. The sheet of ice thus produced 

 is at first nearly opaque ; but when, in the course 

 of a day or two, it has acquired the thickness 

 of a few inches, it becomes transparent, and re- 

 mains so until a fall of snow has obscured the 



VOL. II. h 



