106 GROVE KARL GILBERT— DAVIS [MEM0IE %* A L T xxt 



still gathered in by the roundabout Dirty Devil and therefore yet to be diverted to the more 

 direct subsequent course of Hoxie Creek. Gilbert must surely have been familiar with these 

 details, for he had not only been much concerned in making the model from which the relief 

 map was photographed, but he had previously crossed the Waterpocket flexure four times in 

 different parts of its length. His first sight of it was when going eastward in August, 1875, when 

 he learned to know Hoxie Creek and its horseshoe detour, as detailed in the report and described 

 in abstract here. He next saw the flexure when he was returning westward some 40 miles farther 

 north; his notes of September 1 record that the larger branches of the Dirty Devil there cross the 

 monoclinal valley of the shale belt and cut square through the sandstone escarpment on the east; 

 and that the shale valley, although continuous as a depression for a good number of miles, "is 

 not a line of drainage except for short washes"; these short washes evidently being pairs of em- 

 bryonic subsequent streams as now understood. The two crossings of 1876 did not yield new 

 facts, but they must have made the facts previously noted more f amiliar. Nevertheless, in spite 

 of the knowledge thus gained, in spite of the clear statement of the principle that streams tend 

 to avoid hard strata and to abide in weak strata, announced just before the description of Hoxie 

 Creek above quoted, and in spite of the clear explanation on a later page of the processes by which 

 divides are shifted, no application of the principle and the processes to the facts was made in this 

 particular case ; Hoxie Creek, a typical example of a subsequent stream, was therefore left without 

 physiographic explanation and without genetic name. 



And yet it can not be doubted that Gilbert carried the problem of land sculpture as far 

 forward as he could. His analysis of the processes concerned was carefully conducted; his 

 treatment of the resulting land forms was deliberate and critical. If he did not immediately 

 reach an understanding of subsequent streams and valleys, it must be that that subdivision of 

 the natural history of rivers could not be successfully treated even by his penetrating intellect 

 at the time of his writing. It is of course to be regretted that neither he nor Powell nor any 

 other of his contemporaries was aware that, as has already been intimated, the problem had 

 been successfully solved by Jukes 15 years before in his account of certain streams in southern 

 Ireland, and it may be believed that if Gilbert had had what are called "the advantages" of 

 more thorough collegiate instruction in the erosional chapters of dynamical geology, as that 

 very physiographic subject was understood in his time, his reports would have had a greater 

 number of footnote references to Jukes and other European authors than are now to be found 

 in them. It is, however, also possible that such instruction in dynamical geology as was available 

 in the sixties might have clogged his inquiring mind with conservative prepossessions, and that 

 he might have been thus impeded rather than aided when he had to interpret new phenomena 

 in a new field. But instead of vainly speculating on this might-have-been aspect of the matter, 

 it is more profitable to learn a lesson from the actual facts ; namely, the absence of a competent 

 explanation and of a genetic name for subsequent valleys. The chief lesson here is that progress 

 in physiographic terminology, which goes with progress in physiographic interpretation, is, 

 like progress in general, not accomplished all at once even by a Gilbert, for it is an evolutionary 

 process; and on the other hand, that such progress is not made by minute and imperceptible 

 increments but per saltum, for the advance that Gilbert made over his predecessors was notably 

 great; and finally, that successive leaps of progress are separated by pauses of no progress; for 

 the advance made in the Henry Mountains report was not immediately continued either by its 

 author or by anyone else. This lesson is reenforced by the next. 



BASELEVEL AND TIME 



Inasmuch as Gdbert's adoption of Powell's river-course terminology had manifestly been 

 furthered by intercourse between the two men in Washington, it is truly remarkable that 

 Powell's invaluable term, "baselevel" — now preferably written as a single word, "baselevel" — 

 was not also taken over, for it was conspicuously introduced and employed in Powell's Colorado 

 River report; yet it occurs nowhere in Gilbert's Henry Mountains volume. The phrase "base 

 plane of erosion" is used in a field note under date of July 20, 1875, but not in the report: One 

 may search for the term, baselevel, in vain all through the discussion of erosional processes, 



