were so frequent, that it was difficult to ascend them.
I began to understand Muir's whole new theory, which theory made Tyndall pronounce him the greatest authority on glacial action the world had seen. He pointed out to me the mechanical laws that governed those slow-moving, resistless streams; how they carved their own valleys; how the lower valley and glacier were often the resultant in size and velocity of the two or three glaciers that now formed the branches of the main glaciers; how the harder strata of rock resisted and turned the masses of ice; how the steely ploughshares were often inserted into softer leads and a whole mountain split apart as by a wedge.
Muir would explore all day long, often rising hours before daylight and disappearing among the moun-
