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University of California. 



[Vol. i. 



which has been uplifted from a nearly baseleveled condition to its 

 present altitude, seems beyond question. The rocks of which it is 

 composed are of various ages, of various degrees of hardness, and 

 have been throughout the region so disturbed that their original 

 horizontal condition is practically nowhere to be found. The sur- 

 face of the ancient peneplain consists of the beveled edges of the 

 upturned strata. On the summit of one of the characteristic ridges 

 of the plateau between Usal and Kenny, numerous water-worn peb- 

 bles were found at an elevation of about 1,600 feet, which can only 

 be interpreted as remnants of the stream gravels of the ancient 

 peneplain. 



Former Baselevel Bench Marks. — The uplift of this coastal pene- 

 plain inaugurated a new cycle of geomorphic evolution. A new 

 block was given to the great sculptor Erosion, and he immediately 

 began to shape it. The ancient impotent streams were revivified, 

 and proceeded to sink trenches across the plain. The forces of the 

 ocean strand, tireless in their activity, now became effective for 

 corrasion, and cut broad terraces in the seaward face of the rising 

 block. The extent to which this river trenching and oceanic ter- 

 racing have proceeded, as well as the state of preservation of the 

 terraces and their sea-cliffs, afford a measure, indefinite and relative 

 though it be, of the time since the uplift began. 



In the wave-cut terraces, also, we see that the uplift proceeded 

 by stages. It might be presumed that these stages would also be 

 represented by stream terraces in the valleys. This, however, is 

 true only to a limited extent and chiefly for the earlier and middle- 

 stages of the uplift. From the prevailing absence of important 

 stream terraces in the lower or newer portions of the valleys, the 

 inference seems to be warranted that the stages or stoppages in the 

 upward movement were not of long duration, and that there was 

 not sufficient time for the streams to corrade broad flood-plains. 

 The corrasion of the shore forces is much more vigorous, persistent, 

 and uniform than that of streams, hence the time that sufficed for 

 the sculpture of an ocean terrace was often insufficient to permit of 

 the formation of a corresponding flood-plain. In the marine ter- 

 races, therefore, we find more abundant bench marks of the former 

 baselevels of the coast. The stream terraces when found arc, how- 



