this famous Look Out. The strength of the heavy ice 

 stream which descended the Tenaya "step" was immense. 

 So also was that of the stream which came down the 

 Merced thalweg. Enormous blocks of rock were trans- 

 ported from the faces of the giant "steps," the marvellous 

 system of rock-jointing in the Yosemite permitting this 

 action to be easily accomplished. Of course on such 

 declivities compression and abrasion of structures were 

 altogether subordinate to quarrying and transporting 

 action. The giant "steps" therefore, appear to be almost 

 in the form of a staircase, and in cross-section the channel 

 isat times almost of Y-shape, because the tinge rock masses 

 have simply been hauled oul along dominant fault and joint 

 planes. 



For the Merced, the two "steps" of the Nevada and 

 Vernal Palls show this marvellous quarrying action and 

 consequent absence of abrasion. 



For the Tenaya the deep V-shaped chasm with its im- 

 passable thalweg marks a similar action. 



But at this stage of the "step" recession along the old 

 thalwegs of the Tenaya and Merced channels the Ice Flood 

 disappeared. From the lips of the two huge steps just 

 mentioned topographical features similar to those which 

 once extended vertically above the present Yosemite Valley 

 floor may be seen stretching along both to Lake Tenaya 

 and along the Little Yosemite. Ice swept domes, roches 

 moutonnes, polished pavements and rounded outlines gener- 

 ally evidence the action along the upper broad reaches of 

 the valleys, while rugged walls and beetling precipices 

 equally attest to the much greater power of the descending 

 ice in forming a channel by the removal of a great declivity. 



The earlier stages of glacial decadence were marked by 

 the deposition of moraines in the great ice cutting curves 

 under Cloud's Rest along the Merced Valley. These were 



