Vol. 4] Knopf-Thelen. — Geology of Mineral King. 



233 



feature, whose significance is not entirely plain, is the tendency 

 of the lakelets near the head of any lateral valley to associate 

 in pairs, of which the lower is the complete analogue of the 

 upper; see especially Monarch and Florence Lakes. 



Evidence as to Mechanics of Glacial Erosion. — The tributary 

 glaciers have not evolved the perfect U-profiles so characteristic 

 of the main drainage lines, but are more of the nature of broad 

 and relatively shallow troughs. The troughs upon the western 

 flank of Mineral King are flat-bottomed, of few steps of long 

 tread, and of nearly horizontal floor. On the eastern side the 

 treads are shorter and more numerous, and the floor less regular 

 and often approximating a V-shape. This V is not of post- 

 glacial origin, but is grooved and striated in its upper portion, 

 thus testifying to the efficiency of the subglacial streams. Every- 

 where are abundant evidences of the extreme recency of the 

 glacial evacuation of the region. It is as if the ice had ceased 

 its activity yesterday, and had left incomplete the work it had 

 inaugurated. 



The lateral valleys, particularly that of Monarch Creek, 

 illustrate in no uncertain way the mechanics of the processes 

 concerned in their evolution. The sides of the valleys consist 

 of an ascending series of stopes, like the benches of a quarry, 

 spreading laterally from the stream course as a medial line. The 

 regularity and persistence of this phenomenon is closely de- 

 pendent upon the perfection of the joint-ages, and is often truly 

 remarkable. The jointage to which the bed of the creek is 

 parallel controls the front face of the stopes, while a second 

 jointage intersecting the former at an angle near 90° deter- 

 mines the floor. The salient angle thus formed has been rounded 

 off to a slight extent, but upon the front face of the stope may 

 still be seen partially obliterated inequalities of surface. These 

 are jagged and angular in their innermost recesses and represent 

 uneven fracture planes of the rock masses torn out by the ice 

 from their positions. The front face of the stopes is nearly 

 vertical and may have a height of from six to eight feet, and 

 occasionally even up to fifteen feet. The rocks of Monarch 

 Creek are of stratified character, but similar bench-like forms 



