72 



SCIENCE 



[N. S. Vol. XXV. No. 628 



presented. This latter, called the 'partition 

 process,' occurs when for any reason the 

 swiftest current of a stream is withdrawn 

 from a bank of erosion, with the resulting 

 formation of a sandbar or island not con- 

 tinuous with the eroded banli, and therefore 

 parting the stream. The deeper channel 

 eventually acquires the entire stream, the de- 

 serted channel and former island are added to 

 the floodplain, and the stream has thus moved 

 laterally a certain distance. 



It is shown that West Eiver, swinging 

 laterally by the various processes just noted, 

 and at the same time slowly degrading its 

 previously aggraded valley, has in its down- 

 cutting discovered numerous rock ledges, 

 which have exerted a distinct control iipon the 

 extent and character of the lateral swinging, 

 and hence upon the erosion which has pro- 

 duced the terraces. The paper is abundantly 

 illustrated by diagrams and plates as well as 

 by maps and sections based on original sur- 

 veys, and furnishes an important contribution 

 to the theory that river terraces are not neces- 

 sarily connected with change in stream vol- 

 ume, or with successive uplifts of the region 

 involved. D. W. J. 



FAULT BLOCKS IN THE SIERRA NEVADA 



' The Geomorphic Features of the Middle 

 Kern,' by A. C. Lawson (Bull. Dept. Geol. 

 Univ. Cal., IV., 1906, 397^09), deals with a 

 district of subrecent faulting in the southern 

 Sierra Nevada of California. The case ap- 

 pears to be as follows : A great mountain mass, 

 hereabouts reduced to moderate relief, though 

 hardly smooth enough to deserve the name of 

 peneplain, was raised in the huge fault block 

 of the Sierra Nevada, with a gentle descent to 

 the west ; it was subsequently more or less dis- 

 sected. A local fault in the southern part of 

 the mass, bearing north-northeast, with rela- 

 tive uplift on the west and depression on the 

 east, broke the general westward descent of the 

 range and therefore disturbed the westward 

 flow of the rivers, deflecting some of them to 

 new courses along the fault line, and causing 

 all to aggrade their valleys as they approach 

 the escarpment of the uplift. Breckenbridge 

 mountain is the name given to the uplifted and 



now dissected block, west of the fault line; 

 Walker, Havilah and Hot Springs valleys are 

 aggraded basins lying at the base of the ma- 

 turely dissected fault scarp. The basins are 

 separated by ' spurs ' which come down from 

 the mountains on the east; the spurs appear 

 to be either residual reliefs of pre-faulting 

 form (modified by subsequent erosion), or 

 indications of inequality of faulting, or both. 

 Breckenbridge mountain is described as " an 

 asymmetrical ridge * * * its western slope is 

 exceedingly gentle and descends uniformly 

 towards the great valley [of California]. * * * 

 Its eastern side is a very precipitous mountain 

 front. * * * The mere inspection of the pro- 

 file suggests immediately that the mountain 

 is a tilted orographic block and that its east- 

 ern front is a fault scarp." This vivid de- 

 scription seems to underrate the part played 

 by erosion ; for the front of the block as shown 

 in a photograph slopes only about 25°, and is 

 much scored by large ravines. It would, 

 therefore, seem better to describe the front as 

 ' determined by a fault scarp originally, but 

 now much battered and dissected.' It was the 

 neglect of such specific statement of the work 

 of erosion on the fault-block ranges of the 

 Great Basin that contributed to the misunder- 

 standing of their origin by some observers. 



' The Geomorphogeny of the Tehachapi 

 Valley System ' is another paper by the same 

 author {ihid., 431-462) on a similar problem 

 of greater area and complication. It is of 

 special value because it considers in some de- 

 tail the pre-faulting topography of its dis- 

 trict — a point that has been too generally 

 neglected in studies of this kind. 



W. M. D. 



TECHNIQUE OF PHYSIOGRAPHIC DESCRIPTIONS 



It is a matter of common experience to find 

 difficulty in the appreciation of an article, 

 such as the one outlined in the foregoing note, 

 in which various physiographic features are 

 located with respect to villages like Kernville, 

 Havilah and Vaughn, without the aid of even 

 an outline map. Unimportant villages, pre- 

 sumably unknown outside of their own state — 

 and probably not known all through so large a 

 state as California — have no guiding value to 



