2 



courses of the ravine and its tributaries, the probable origin of the 

 ravine, and its present physiography. The McLeish ravine is formed 

 by the confluence of two gullies, the heads of which, if measured in 

 straight distance, are each about 2000 feet inland. From the junc- 

 tion of the two gullies the ravine has an almost easterly direction for 

 about 1500 feet, until it reaches its main tributary from the south, 

 when it continues in a northeasterly direction for about 800 feet to 

 the point where it empties into the lake. From the south, in addition 

 to the main tributary, the ravine receives a number of small gullies. 



Physiographers have summarized under three heads the succes- 

 sive stages in the cycle of the development of such a ravine as the 

 one here considered : the V-shaped valley, with slopes normally con- 

 vex; the U-shaped valley, a stage of development where detritus 

 descending the slopes is not all carried away by the stream, and con- 

 sequently the valley is being widened faster than it is deepened ; and, 

 finally, the valley with a broad bottom, in which transformation is 

 affected partly by erosion and partly by deposition in the ravine. The 

 tributaries of the McLeish ravine are mostly in the first stage of the 

 cycle, while the main course of the ravine shows that it is passing 

 from the V-shaped stage into the U-shaped stage. 



It is altogether likely that this ravine had its infant development 

 accelerated by swampy depressions in the upland near to the lake. 

 Such swamps or marshes within reasonable distance from the head 

 of the cliff of the lake shore would, through seepage, make materials 

 between them and the lake shore so mobile that the head of the gully 

 would work inland with unusual rapidity. The influence of such de- 

 pressions in ravine formation can at present be seen in the vicinity 

 of Glencoe. 



In the weekly visits to this ravine, the physiographic changes due 

 to weathering, wash, and lateral corrasion were decidedly noticeable. 

 Some of the records made at the time of observation read as follows : 

 ( 1 ) — during a heavy rain — small streams of clay are flowing leisurely 

 to the bottom of the stream; (2) it will be only a matter of a rela- 

 tively short time when two large hard-maple trees will become so 

 undermined by the streams caused by heavy rains as to fall across the 

 channel; (3) a large slump of clay has been deposited at the bottom 

 of the ravine during the preceding week, due to the undermining 

 action of the stream and to the percolating of the water through the 

 soil above the cavity; (4) in following the ravine, from the point 

 where the main tributary enters, to its mouth, a gradation of detritus 

 ranging from boulders and cobblestones to sand is passed (PI. I, Fig. 

 1) ; (5) the waves of the lake usually maintain a bar of shingle and 

 sand across the mouth of the ravine, which results in the formation 



