In the following pages I propose to set forth the results of observations made in that part of the Cordilleran system which lies within the limits of the United States, excluding Alaska. The main end in view is to exhibit the history of the erosive processes in that region with reference to successive changes in climate during the later geological periods. Incidentally, reference will be made to the general conditions of erosion in mountainous countries and to the effects of alternating plentiful and scanty rainfall on the forms of valleys as well as the influence of the volcanic ejections which have occurred in the Cordilleras since the existing topography began to be developed.
Although the results of the inquiries which are recorded below represent a considerable amount of labor, including journeys aggregating a distance of more than 10,000 miles within the area above noted, they must be regarded as . . .