REPORT OF TEE CHIEF ASTRONOMER 



593 



SESSIONAL PAPER No. 25a 



glaciers streamed away to merge with the still heavier trunk glaciers moving 

 along the Pasayten, Skagit, and other master valleys. 



In some of the cirques of the range there occur ridges of coarse rock- 

 debris such as that illustrated in Plate 57. These ridges are from one to three 

 hundred yards or more in length and are best developed along the southwest and 

 south walls of northerly facing cirques. The axis of each ridge is generally 

 somewhat curved in ground-plan, with the concavity facing the concavity of 

 the cirque-wall. The height of the wall of angular rock fragments varies from 

 five feet or less to thirty feet or more. In each case most of the accumulation 

 of debris evidently took place at such times as the cirque was occupied by a 

 heavy bank of snow. This was drifted to specially great depths (fifty feet or 

 more) against the relatively shaded sides of the cirque. Prom the cliffs above 



HEAD OF 

 CIRQUE 



Figure 41. — Diagrammatic section showing origin of a " winter-tahis ridge ". 



the snow!-bank, frost rifted away masses of rock which fell upon the snowdrift, 

 to roll down its steep surface and lodge at its foot, and thus clear of the cirque 

 wall. This action has, in places, been continued long enough to form long and 

 quite remarkable piles of rock-fragments on the floors of the cirques. Since 

 these special accumulations of debris are dependent on the formation of heavy 

 snow-banks and on specially rapid frost-action before the summer heat has 

 melted the snow in large measure, the wall-like piles may be called ' winter- 

 talus ridges ' (Pig. 41) . Other fine examples were observed in the glacial 

 amphitheatres of the Rocky Mountain ranges. 



Hozomeen Range. 



The extensive massif culminating in Castle Peak was one of the 

 centres of ice-dispersal during the heavy glaciation of the Hozomeen 

 range. Valley glaciers from 1,000 to 2,500 feet deep moved out from the 

 central snowfield toward all four quarters of the compass. When the sheets 



