6l2 



ELLSWORTH HUNTINGTON 



.''.-V,::-. 



glaciers a dry epoch ensued, during which a salt lake filled the basin, 

 standing at a low level long enough to allow the accumulation of a fan 

 above the rock-lip. Then, presumably upon the advent of a glacial 

 epoch, the lake rose until at a height of 200 feet above the present 

 level it began to overflow across the fan. From that time onward the 

 water fell, pausing but a short time at each of the levels where the 

 six or seven faint strands appear. One reason for the fall in the 

 lake-level was doubtless the cutting away of the fan at the outlet, 

 but as the latter appears to have been of uniform texture, this will 

 not account for the fluctuations in the rate of fall as indicated by 



the strands. Another reason was the 

 gradual desiccation which, as is shown 

 below, finally reduced the lake to its last 

 low level previous to that of today. The 

 desiccation probably proceeded at a fluc- 

 tuating rate, as we shall see to have been 

 the case in a still later epoch, and the 

 terraces and strands may be attributed 

 to this. 



Evidence of the low level reached by 

 the lake after the formation of the strands 

 just described is found in the present fan 

 at the outlet and in the deposits exposed 

 in cuttings made by streams in other fans 

 along the lake shore. In the outlet valley, 

 as we ha\e already seen, the older fan was cut away during a glacial 

 epoch. The present fan could not have accumulated unless the outlet 

 stream was greatly reduced in size or ceased to flow; that is, unless 

 the climate became somewhat arid. More conclusive evidence of the 

 low strand of the lake is found at Tukkung, along the Lamle brook, 

 where the two sections illustrated in Fig. 11 lie about 100 yards 

 apart, their tops being about 20 feet above the present lake-level. 

 The deposits above the unconformity (A-B) consist of lacustrine 

 marls, more or less sahne, containing fossil shells and plants; while 

 those below are fluviatile deposits of sand and gravel hke that which 

 the stream now carries. The folding and crumpling to which the 

 gravels have been subjected is like that which is today produced on 



Fig. II. — Sections of the 

 fan at Tukkung. 



A, £ = Unconformity. 



Be = Gravel beach. 



/,<; = Lacustrine deposits. 



56 = Subaerial (fluvial) deposits. 



