250 National Geographic Magazine. 



wig-Holstein affair compared to the Goth- and Hun-like depreda- 

 tions of the greater streams in earlier cycles. 



The character of the streams and their valleys as they now 

 exist is strikingly dependent in many ways on the relation of the 

 incipient quaternary cycle to the longer cycles of the past. No 

 lakes occur, exception being made only of the relatively small 

 ponds due to drift obstruction within the glaciated area. Water- 

 falls are found only at the headwaters of small streams in the 

 plateau district, exception again being made only for certain cases 

 of larger streams that have been thrown from their pre-glacial 

 courses by drift barriers, and which are now in a very immature 

 state on their new lines of flow. The small valleys of this cycle 

 are shallow and narrow, always of a size strictly proportional to 

 the volume of the stream and the hardness of the enclosing rocks, 

 exception being made only in the case of post-glacial gorges 

 whose streams have been displaced from their pre-glacial channels. 

 The terraces that are seen, especially on the streams that flow in 

 or from the glaciated district, are merely a temporary and subor- 

 dinate complication of the general development of the valleys. 

 In the region that has been here considered, the streams have 

 been seldom much displaced from their pre-glacial channels ; but 

 in the northwestern part of the State, where the drift in the 

 valleys seems to be heavier, more serious disturbance of pre- 

 glacial courses is reported. The facts here referred to in regard 

 to lakes, falls, gorges, terraces and displaced streams are to be 

 found in the various volumes of the Second Geological Survey of 

 the State ;* in regard to the terraces and the estuarine deflections 

 of the Delaware and Susquehanna, reference should be made also 

 to McGee's studies.f 



42. Doubtful cases. — It is hardly necessary to state that there 

 are many facts for which no satisfactory explanation is fouijd 

 under the theory of adjustments that we have been considering. 

 Some will certainly include the location of the Susquehanna on 

 the points of the Pocono synclines under this categoiy ; all must 

 feel that such a location savors of an antecedent origin. The 

 same is true of the examples of the alignment of water-gaps 

 found on certain streams ; for example, the four gaps cut in the 



* Especially Carll, Reports Is, I4 ; White, Reports G5, Ge ; Lewis, 

 Report Z. 



f Amer. Journ. Science, xxxv, 1888, 367, 448 ; Seventh Annual Rep. 

 U. S. G. S., 1888, 545. 



