TRIBUTARY RAVINES. 131 



Some of the lesser ravines which run in on 

 either side present a totally different appearance, 

 although they must formerly have served as tribu- 

 tary watercourses to the main stream. One of 

 these, near the mouth of the gorge, which I care- 

 fully explored, was not more than eight or ten feet 

 wide, and hecame still more contracted as I clam- 

 bered up its irregular ascent, over debris of large 

 stones and sharp, angular blocks that lay in the 

 very centre of its bed. The steep sides of this 

 cleft could not have been less than thirty feet high, 

 and the escarpment on either side was quite per- 

 pendicular, reminding me of one of those narrow 

 streets of lofty houses, in certain old fortified 

 German towns, that debouche at the bottom of a 

 steep hill into the principal thoroughfare. The 

 walls of the fissure to a great height exhibited 

 a mass of conglomerate, but above this I perceived 

 that the upper portion of the cliff was composed 

 of the till, or glacial drift, overlaying the more 

 ancient formation, of a somewhat lighter colour, 

 but nearly resembling it in character and consist- 

 ence. The depth of these beds varied remark- 

 ably. Immediately over my head the deposit was 

 of unusual thickness, without any traces of strati- 

 fication, and containing angular stones, rocks, and 



