Yosemite National Park 



195 



ledges and transported long distances is shown by the study 

 of the rocks themselves. Moraines tell their own story. The 

 ultimate causes of many natural phenomena are as yet unknown. 

 The stages in the glacial history of the Sierra region are 

 marked by the results of the action of the ice itself. Deposits 

 made by the ice, moraines consisting of earth materials carried 

 by the ice and thrown down when it melted, tell unmistakably 

 of the movements of the ice and the work done by it in its slow 



Photo by F. E. Uatthes, U. S. Geol. Survey 

 FIG. 59. Crest of moraine of Wisconsin stage. 



but relentless progress. Terminal moraines, the dumping- 

 grounds where rock fragments of all sizes boulders, gravel, 

 sand, and clay are mixed in confused order, mark the ends or 

 limits beyond which the ice did not go. These are the places 

 where melting from the sun's heat balanced the onward move- 

 ment of the ice mass. The character of the work done by the 

 moving ice is shown in marks it left in its path. Fragments of 

 rock carried by the ice, plucked from rock floors and walls, 

 were rounded and ground to powder. These, held in the vise- 



