S44 THE JOURNAL OF GEOLOGY. 



more symmetrical systems. Abrupt turns and striking detours 

 of streams are, on the whole, less frequent, 1 though this is not 

 illustrated by limited areas everywhere. Within the drift area 

 of North America, rapids, falls, and other evidences of youth- 

 ful drainage are much more common than in adjacent driftless 

 areas of comparable altitudes. The elevations between the 

 valleys are more continuous in the driftless areas, unless the 

 drainage system is so far advanced in its life-history as to have 

 notched the inter-stream ridges, or to have cut them into isolated 

 hills. The elevations and valleys stand in more definite and con- 

 stant relations to each other ; that is, the topography of the 

 driftless country is a topography the details of which have been 

 fashioned mainly by running water. 



If it be true, as, on the whole, it probably is, that the drift 

 territory has less relief than the driftless for corresponding alti- 

 tudes, it is also true that its surface is often more "choppy," the 

 hills being shorter and more noticeably huddled together. This 

 characteristic is popularly recognized in such names as " short 

 hills," "knobs," 2 etc., names which have been locally used 

 because of the striking contrast in shape between the discon- 

 tinuous hills of drift, and the associated hills of greater length 

 composed of solid rock (see Fig. 2) . The choppiness of surface is 

 by no means co-extensive with the drift. Where it is present, the 

 ■drift, rather than the underlying rock, is the controlling element 

 in the present topography. Drift hills are sometimes low and 

 symmetrical in form, and their slopes gentle. They are sometimes 

 more or less systematic in arrangement over considerable areas, 

 but even then their forms do not generally stand in any definite 

 relation to river valleys. Hills which are only drift-coated 

 may bear a more or less obvious relation to the valleys, but 

 hills composed entirely of drift are measurably independent of 

 them. 



1 The abrupt turns of streams in their flood plains is not here taken into account. 



2 The name " Short Hills " has been given to a village in New Jersey where the sur- 

 face is of the character here referred to. The term "knobs" is frequently applied to 

 the abrupt and closely set drift hillocks. This term has also been popularly used in 

 other relations to designate a very different type of topography. 



