February 15, 1895.] 



SCIENCE. 



179 



from the formative streams, are, perhaps, to 

 be considered as of the nature of terraces 

 marking the flood plains of a past stage of 

 erosion" (p. 322, 328). Change of altitude 

 of the region, or in other words, change of 

 baselevel. is not referred to as essentiallj' 

 involved in the problem. 



The plateau surface, sloping to the west 

 and terminating eastward in an escarpment 

 Carboniferous strata, seems to depend on the 

 greater resistance of these strata. It might 

 be called a structural plain ; a stripped sur- 

 face on which general denudation has hesi- 

 tated by reason of the endurance of the ex- 

 posed strata, although the streams have 

 deeply trenched it. 



With the prairie plains the case is difter- 

 ent, for much of their area " is underlain by 

 coal measure rocks, which are readilj' acted 

 on by sub-aerial agents of erosion" (p. 

 323) . If the streams of the region were not 

 enclosed by steep- sided valleys, but wander- 

 ed across the plains in channels hardly be- 

 neath the general surface level, then it 

 might be admitted that the whole surface 

 would waste away about as fast as the 

 streams degraded their courses. But as the 

 streams are in well-enclosed valleys, it does 

 not seem logical to admit that the inter- 

 stream plains can have wasted as fast as the 

 valley forces. If the streams of the region 

 even now distinctly incise its surface, all 

 the more strongly must they have done so 

 before long continued denudation had re- 

 duced its original altitude to its present 

 altitude. The steep valley sides should 

 long ago have been ravined, and the inter- 

 stream plains should thus have been un- 

 evenly dissected. If this process had been 

 long in progress, the region might already 

 have reached or i>assed through the stage of 

 most varied relief — topographical maturity : 

 but it could not have attained an even sur- 

 face distinctly above the level of its streams. 

 Similarly, it does not seem admissible to 

 suppose that streams, which are now run- 



ning in rather narrow, steep-walled valleys, 

 should ever, when still higher above base- 

 level, have had broad flood-plained valleys, 

 beneath which they have incised the narrow 

 existing vallej-s, yet without being prompt- 

 ed to this change of behavior by any change 

 of altitude in the region. 



A decision as to the origin of these plains 

 must be left to workers on the ground ; but 

 opinion as to the sufficiency of the j^rocess 

 suggested for their production may be formed 

 by any one who has familiarized himself 

 with the general principles of denudation 

 here involved. In the writer's mind Wins- 

 low's hypothesis does not invalidate the 

 generally current principles of the base- 

 leveling theory. 



gannett's manual of topographic 



METHODS. 



The general principle that the topo- 

 grapher should be well trained in physio- 

 graphy is strongly affirmed in CJannett's 

 Manual of Topogi-aphic Methods ( Monogr. 

 XXII., IT. S. Geol. Survey, 1S93, issued in 

 1894). The volume contains a concise ac- 

 count of the surveys thus far undertaken 

 in the United States ; an account of the 

 map now in progress by the U. S. Geological 

 Survey, this containing much of interest to 

 the geographical reader; and a treatment 

 of the more technical matters of astronom- 

 ical determination of position, horizontal 

 location, secondary triangulation, sketch- 

 ing, and office work. In the chapter on 

 sketching, there is an interesting discussion 

 of the origin of topographic forms, with 

 illustrations taken from various map 

 sheets in the Survey office; this discussion 

 being introduced 'as an aid in the interpre- 

 tation of the various topographic forms 

 which present themselves' to the topo- 

 grapher. Here we read the sound state- 

 ment that "it is in the matter of generaliza- 

 tion that the judgment of the topographer 

 is most severelv tested. He must be able 



