TOPOGRAPHY OF THE PACIFIC COAST. 49 



baselevel. The removal of material was chiefly by solution, 

 and the insoluble residuary material thus set free by the disin- 

 tegration of the rocks accumulated to considerable depths upon 

 the land. 



The long period during which the land of northern California 

 remained comparatively stationary, and which enabled the 

 streams in many parts of that region to practically complete 

 their cycles of erosion from youth to old age, was brought to a 

 close by the initiation of an orogenic movement which generally 

 increased the grade of the streams upon the western slope of the 

 Sierra Nevada. At first the differential change of level was very 

 moderate and increased the declivity of the streams but little,, 

 but being long continued it became in time revolutionary in its 

 effects, and finally, accompanied by extensive volcanic eruptions,, 

 gave birth to the High Sierra of to-day with the deep canons 

 upon'its western slope. 



The first result of this change of slope was to rejuvenate the 

 streams and invigorate erosion. On account of surface deforma- 

 tion which must have accompanied the upheaval of such a large 

 mass as the Sierra, the stream grades would be differently affected 

 even along the same channel, and in fact, as Mr. Lindgren has 

 pointed out, in at least one case, owing to direction of flow, the 

 stream grade has been not only diminished but reversed.^ 



The country being covered by a thick coating of soft residu- 

 ary material, of which the great mass was fine particles, erosion 

 was easy. There were coarser fragments of quartz, largely vein 

 matter, as well as boulders of disintegration which had withstood 

 the chemical changes. The streams readily became loaded not 

 only to their full capacity but overloaded with the mass of fine 

 material, and were thus forced to deposit the coarser particles. 

 The grains and fragments not quite suspendable under the condi- 

 tions of load were rolled along the bottom and rounded by 

 attrition. 



In this way the old channels of the baselevel period became 

 filled with gravel of which by far the larger part is quartz. In 



' Bui. Geol. Soc. of Am., Vol. 4, p. 281. 



