294 E. C. ANDREWS. 



smaller enclosed forms. This phenomenon was also noticed 

 by the writer in British Columbia. 



A very common feature of these steep, deep and broad- 

 floored upper canons is the existence of a line, or series of 

 lines, which may be seen to be strongly marked along the 

 lower portion of the valley sides. The lines are approxi- 

 mately horizontal and in detail they appear to consist of 

 small benches associated with lines of cliff erosion. Below 

 a bench or erosion line of this kind the valley slopes gener- 

 ally become less regular than those above the erosion lines. 

 These lines are very pronounced along channels of steep 

 slope and in valley constrictions, while they fade away in 

 valley " broads," where lines and terraces of moraines are 

 found instead of the lines of erosion (e.g., at Rock Oanon). 

 Frequently also one may see a line of such erosion extend- 

 ing completely along the side of the main valley constriction 

 and being joined at accordant slope by a similar line descend- 

 ing a side valley wall. This line also forms the upper limit 

 of the small cirque forms which lie within the larger and 

 older amphitheatres or cirques. The line of erosion com- 

 mences with a steep descent, which it maintains around 

 the cirque and then the cirque form being passed it makes 

 a more gentle descent, such declining slope, however, being 

 proportioned to the steepness of the channel floor. 



These slight benches appear also to be fairly evenly 

 laden with moraine-like debris, while upon this in turn 

 are scattered talus cones, derived from the weathered 

 material of the steep upper slopes. In conclusion it may 

 be mentioned that these canons which possess such decided 

 evidences of former strong glacial action have now only 

 tiny inactive glaciers at their heads — glaciers preserving 

 a banded appearance from head to foot. 



Significance of observations in the Sierras. — The higher 

 summits of the Sierras appear to represent residuals of an 



