78 THE POPULAR SCIENCE MONTHLY 



its powerful volume down the deep-gashed gorge of Tenaya Creek into 

 the Yosemite Valley. Professor Le Conte estimated that the main 

 Tuolumne glacier ranged in thickness from a thousand feet in the 

 upper meadows of the modern stream to half a mile in the brimming 

 basin of the Hetch Hetchy. Its length he measured as having been fully 

 forty miles. In the upper canon of the main Merced, Le Conte and 

 Muir studied the striations of grinding ice recorded on every outcrop- 

 ping surface, particularly in the "hanging valley" of "Little Yosem- 

 ite." Together with the Tenaya glacier, the Merced River of ice 

 mingled at the upper end of the Yosemite Valley, proper, to form a grand 

 glacier which Le Conte believed was the most potent factor in the carv- 

 ing of the U-shaped trough of the Yosemite. And, despite the doubts 

 of Whitney and Russell, Le Conte pointed as prima facie proof the 

 remaining medial moraine at the base of Half Dome near the junction 

 of the two reputed rivers of ice. 



Several Geological Survey parties have been sent to solve the riddle 

 of this Sphinx of the Sierras, but still no explanation of the origin 

 of the Yosemite has won the general recognition of geologists or recon- 

 ciled their differences of opinion. Mr. Francois E. Matthes, of the 

 Survey, in his recent monograph, "The Origin of the Yosemite and 

 Hetch Hetchy Valleys," approaches the problem along the following un- 

 biased lines of logical observation and deduction. Like Le Conte, he lays 

 great stress upon the phases of erosion in the more fissured zones. He ac- 

 cepts the general theory of the uptilting of the Sierra block during the 

 late Tertiary period by volcanic levers, but gives little credence to the 

 subsidence dictum of Whitney. As an ardent advocate of the glacial 

 theory, he traces the apparent agency of ice in the evidence of over- 

 deepened rock-basins and quarried canons like the steep gorge of Tenaya 

 Creek. This striking instance is a graphic illustration of the excava- 

 tion of a yielding mass of perpendicular cleavage set between walls of 

 massive and adamantine granite. In brief, he argues that the Yosem- 

 ite and Hetch Hetchy Valleys have been developed by an early system 

 of rapidly-eroding streams; then "greatly deepened and enlarged by 

 repeated ice invasions which modelled in the rough. The finer fash- 

 ioned details- of diversified sculpturing he attributes to more recent 

 aqueous agencies and fracturing by frost and aerial forces. Far the 

 most convincing evidence of the former glaeiation of the Yosemite 

 Valley he finds in the apparent scooping out of the rock-basin of the 

 Yosemite to the depth of approximately 500 feet. This is confirmed, 

 he contends, by the absence of sills of bed-rock, such as are usually seen 

 outcropping among ordinary watercourses. Another important factor 

 in the leveling of the floor of the valley he sees in the signs of several 

 advances and recessions of terminal moraines across the bottom of this 

 basin, in which process they were arranged in local ridges at frequent 

 intervals. The most conspicuous terminal moraine is that which still 



