VI THE GORGE OF THE AAR AND ITS TEACHINGS 135 



temperature, the upper portions of these canons have been 

 greatly widened and everywhere exhibit surfaces of frac- 

 ture and sub-aerial erosion, largely due to the gi'eat 

 and rapid alternations of temperature to which they are 

 exposed. 



If this view of the formation of these water- worn gorges 

 is correct they ought to be found only in regions which 

 have been recently glaciated, and it will be interesting to 

 inquire if this is the case. In our own country we have 

 many small gorges of this character, in Wales, the Lake 

 District, and Scotland, that of Dungeon Gill, in West- 

 moreland, being an example ; but none are to be found in 

 decidedly non-glaciated areas, such as Devonshire, though 

 narrow ravines are common enough. So in the Northern 

 United States there are many such gorges, the Ausable 

 ChasQi in the Adirondacks, and Watkin Glen near Seneca 

 Lake are well-known tourist resorts ; but in the Southern 

 States, beyond the glaciated area, there are no similar 

 gorges, although the southern AUeghanies are loftier than 

 farther north, and contain much gi^and and picturesque 

 mountain scenery and many waterfalls and deep ravines, 

 but these are all of the rugged and weathered type. 



The best test, however, of these vertical gorges being 

 really produced by sub-glacial torrents, will be to ascertain 

 whether they occur in any extensive tropical mountain- 

 region where there has certainly been no recent glaciation. 

 Brazil seemed to me to be such a country, of great 

 extent, mountainous throughout a large part of its area, 

 and very thoroughly explored. I therefore wrote to my 

 friend, Professor Branner, of the Stanford University, 

 California, who spent three years in making a geological 

 survey of Brazil, visiting every part of the country and 

 paying special attention to all the physical features of the 

 surface. 



In reply to my inquiry, Professor Branner writes as 

 follows : — 



"What you say of certain channels in Switzerland is 

 certainly most interesting. . . I recall the fact that there 

 are just such gorges at Grindelwald and at Zermatt open- 

 ing from beneath the glaciers. I have turned over in my 



