PHYSICAL GEOGRAPHY IN THE UNIVERSITY. 87 



tion already seen on its surface. While the building of a vol- 

 canic cone is spasmodic, almost instantaneous, the uplift of a 

 great mountain is rather slow ; its uplift is brief only when com- 

 pared to the duration of the destructive C3'cle on which it thereby 

 enters. When first describing the cycle, it was implied that the 

 destructive forces make no beginning until the constructional 

 forces have completed their work. The view of St. Elias cor- 

 rects that false idea. Several plains follow ; all dead level ; all 

 ending in even sky lines. The Llano Estacado of Texas, the 

 lava deserts of southern Idaho, the littoral plain of southern 

 New Jersey, the lacustrine plain of the Red River of the North. 

 The areas included in these views show no signs whatever of 

 destructive processes ; the surfaces are essentially as flat as when 

 they were born. A pair of drumlins in Boston harbor, and a glacial 

 sand-plain in Newtonville, Mass., as represented in a model by 

 Mr. Gulliver,^ introduce examples of peculiar constructional 

 forms ; and as the more intelligent members of the class soon 

 point out, these might be as fairly included under a considera- 

 tion of destructional processes as of constructional processes ; 

 for they really belong among the "forms taken by the waste of 

 the land on its way to the sea," under certain special conditions, 

 and they will be reviewed in a later chapter of the course 

 under that heading. The drumlins and the sand-plain may also 

 be regarded merely as evidence of a glacial accident during the 

 denudation of the New England plateau. 



Passing next to illustrations of young destructional forms, 

 Mt. Shasta is exhibited, with great gulleys worn down its flanks. 

 It is at once pointed out that these gulleys follow lines of con- 

 structional slope ; that they began as the paths of constructional 

 streams, defined by some accidental irregularity in the form of 

 the volcanic cone ; and that they are now slightly advanced in 

 their consequent growth. The Mancos canyon in Colorado illus- 

 trates the beginning of the dissection of a plateau ; the conse- 

 quent stream having here cut down a steep-sided consequent 

 valley, but apparently not having yet graded its slope. A 



' See this Journal, Vol. I., p. Soi. 



