c;iian(;es of surface. 249 



separated from the beach by a few feet of open water. Even when tlie 

 lake is in a state of very considerable agitation scarcely a ripple reaches 

 the shore thus protected, and not only is the erosion of the banks in great 

 measure prevented, but sedimentation is fovored, so that in some places the 

 shore appears to be growing into the lake by the accnnuilation of tule 

 roots and sediment. On tlie whole, therefore, the lowering of the lake 

 level in comparatively recent times is not improbably the result of the ero- 

 sion of the bed of Cache Creek, assisted by a very gradual and gentle tilt- 

 ing of the whole region toward the east or southeast. 



Certain limited orographical changes have unquestionably taken place 

 about the lake in very recent times. At the end of Elgin Point is a steep 

 bank, consisting of uncompacted strata of material precisely similar to that 

 found on the old lake bottom areas at the Sulphur Bank, in Big Valley, 

 and below the high-water mark of the lake. It consists of mud, in which 

 pebbles of metamorphic rock and of later andesite are abundant. In the 

 lower strata of this bank, which is about one hundred and fifty feet high, 

 scoriaceous forms of andesite occur, which are no longer to be met with 

 on the surface in the neigliborhood. The southern side is a curved slope 

 parallel to the planes of stratification and essentially unsculptured by wa- 

 ter, and the bank would seem to represent an- uplift of about the same 

 date as the finely preserved craters near Sulphur Bank. If the hypothesis 

 suggested with regard to the formation of the basin occupied by Little 

 Borax Lake be correct, this uplift was probably its concomitant. These 

 recent strata rest in part upon metamorphic rocks and in part upon the 

 andesite which constitutes the main mass of Elgin Point. A very similar 

 bank of the same date, but less well exposed for study, occupies the south 

 side of the entrance to Upper Lake. 



It is the inevitable fate of lakes to be filled with sediments to a dead 

 level, but, as the evidence seemed to be that the sediments of Clear Lake 

 are not of great thickness, it appeared to me desirable to examine the to- 

 pography of the bottom. Several hundred soundings were made for this 

 purpose, the results of which are shown in the subaqueous contours on 

 the map of the lake. From these it appears that the water is deepest near 

 the narrows, as would be the case if the lake occupied valleys of erosion 



