842 THE JOURNAL OF GEOLOGY. 



the topography of the underlying rock. Yet, in spite of all these 

 exceptions, the presence of undrained depressions associated 

 with elevations which, roughly speaking, are their counterparts, 

 is one of the most distinctive features of drift topography. The 

 topography of the drift is in sharp contrast to the topography 

 developed by river erosion, for in regions whose surfaces are 

 fashioned by river erosion the depressions are valleys, and each 

 has an outlet. Every tributary valley leads to a lower, and the 

 lowest leads to a lake, to an inland basin, or to the sea. 



When the surface of the drift is rough, the roughness is 

 dependent in part on the amount of relief, but more especially 

 on the abruptness of the hills and hollows, and the closeness of 

 their association areally. Where they have steep slopes and are 

 close-set, even with but moderate relief, the topography appears 

 rough. Where they are farther from one another, and possess 

 gentler slopes, the topography may appear much less rough, 

 even though the relief within broader areal limits be equally 

 great. The topography of the drift, could it be distinctly sepa- 

 rated from the topography of drift-covered areas, would be found 

 to be measurably independent of the topography of the sub- 

 jacent rock. 



The Topography of the Drift-Covered Areas. 



It is of consequence to distinguish between the topography 

 of driftless and drift-covered territory. The topography of the 

 latter is often, but not always, strikingly unlike that of the 

 former. The topography of driftless territory varies within cer- 

 tain limits, and the topography of drift-covered territory varies 

 within certain other limits. Sometimes the two types of topog- 

 raphy vary toward a common limit. Under such circumstances 

 they may closely simulate each other. In general it may be said 

 that the most distinctive difference between the topographies of 

 drift and driftless areas is the more perfect and more systematic 

 development of the drainage lines upon the latter. This is made 

 obvious in one way by the abundance of marshes, ponds, and 

 lakes in the drift area, in contrast with their scarcity without. 



