MOUNT RAINIER 



erect, angular blocks and fantastic obelisks. Below 

 each dome there is, as a rule, a deep hollow partly in- 

 closed by trailing ice ridges, analogous to the whirl- 

 ing eddy that occurs normally below a bowlder in a 

 brook. Thus does a glacier simulate a stream of 

 water even in its minor details. 



The domes of the Winthrop Glacier measure 50 to 

 60 feet in height. A sample of the kind of obstruction 

 that produces them appears, as if specially provided 

 to satisfy human curiosity, near the terminus of the 

 glacier. There one may see, close to the west wall of 

 the troughlike bed, a projecting rock mass, rounded 

 and smoothly polished, over which the glacier rode but 

 a short time ago. 



Another feature of interest sometimes met with on 

 the Winthrop Glacier, and for that matter also on the 

 other ice streams of Mount Rainier, are the "glacier 

 tables." These consist of slabs of rock mounted each 

 on a pedestal of snow and producing the effect of huge 

 toadstools. The slabs are always of large size, while 

 the pedestals vary from a few inches to several feet 

 in height. 



The origin of the rocks may be traced to cliffs of 

 incoherent volcanic materials that disintegrate under 

 the frequent alternations of frost and thaw and send 

 down periodic rock avalanches, the larger fragments 

 of which bound out far upon the glacier's surface. 



The snow immediately under these large fragments 

 is effectually protected from the sun and does not melt, 

 while the surrounding snow, being unprotected, is 

 constantly wasting away, often at the rate of several 

 inches per day. Thus in time each rock is left poised 

 on a column of its own conserving. There is, how- 

 ever, a limit to the height which such a column can 

 attain, for as soon as it begins to exceed a certain 

 height the protecting shadow of the capping stone no 

 longer reaches down to the base of the pedestal and 

 the slanting rays of the sun soon undermine it. More 



228 



