acadkmv 0F SCIENCES] WHEELER SURVEY 55 



In view of this principle, a physiographic description does not go far enough in merely 

 saying that an observed land form results from the action of erosion, undefined in amount and 

 stage, upon a structural mass, unspecified as to its surface form and attitude at the time of its 

 last deformation or upheaval. It is necessary, if the description is to be clearly intelligible, to 

 explain the observed or actual form by the systematic action of sculpturing agencies through a 

 certain period of time upon a structural mass, the surface of which had a certain form in a 

 a certain attitude at the beginning of the erosional period under consideration. In dealing 

 with the upheaval or fracture of a crustal mass, a geologist might be satisfied to state the 

 measure, date, and cause of the movement; but if such upheaval or fracture is to enter properly 

 into a physiographic description, it must constitute the second member in a threefold sequence 

 of treatment: The first member must explain the surface form that the crustal mass had acquired 

 before it was deformed; the second member must then define the effect that the deformation 

 had upon the predeformational surface form as well as upon the crustal mass; and the third 

 member must state how far the predeformational forms have been destroyed and new forms 

 have been introduced by later erosion. This explanation may seem so plain to those who are 

 accustomed to employ the threefold sequence of treatment that it involves, as to be hardly 

 worth announcing here; but unhappily this scheme of treatment is still unknown to or neglected 

 by certain geologists — to say nothing of physiographers — who undertake to write physiographic 

 descriptions; and as a consequence then descriptions are imperfectly intelligible. 



AGE AND STRUCTURE OF THE RANGES: FIRST WHEELER REPORT 



If Gilbert's first report is now examined with the principles and methods outlined in 

 the preceding paragraphs in mind, it will prove interesting to search out the successive an- 

 nouncements of his theoretical views on the origin of his mountains, even though the incom- 

 pleteness of their statement may occasion surprise. It may be here explained, by way 

 of introduction, that very little is to be found concerning the theoretical aspects of the basin- 

 range problem in any of the three seasons' notebooks. Where the problem was touched 

 upon at all in the field records, the treatment is either so brief or so vague as to give little 

 indication of the many questions that it involves. For example, it was noted on September 

 15, 1872, that the structure of a range near Beaver River in southwestern Utah led "to the 

 opinion that the whole is in general a monoclinal uplift with Dip to the W. & composed of 

 the quartzite & limestone of the Silurian. " An earlier and somewhat more explicit statement 

 is made regarding the Fish Spring and House Ranges, nearer the Utah-Nevada boundary, 

 where they are both treated under the latter name. The northern and smaller member, or Fish 

 Spring Range, was recognized to have a westward dip with an east-facing escarpment, while 

 the much longer southern member, or House Range, was described as having an eastward 

 dip with a west-facing escarpment; the two monoclinal masses being on opposite sides of the 

 nearly direct line on which the two escarpments fall. These facts led to an important con- 

 clusion noted on August 25, 1872: 



The peculiar characters of the House Range suggest that it marks a N-S crack the western lip of which 

 [Fish Spring Range] is uplifted North of Dry Pass [Sand Pass on the topographic map the Fish Springs quad- 

 rangle] while the eastern lip [the House Range proper] is uplifted S of the pass. We could see yesterday that 

 the two uplifts are not quite in line, but have an offset at Dry Pass. 



Furthermore, two months later Gilbert's party was in the plateau province and had 

 followed the canyon of Kanab Creek southward to its junction with the canyon of the Colo- 

 rado, where he found by the way, two of Major Powell's boats "& a great variety of tilings 

 scattered about on the bank, " and where the structure and erosion of the plateau afforded 

 matter for many pages of notes; and there an unexpected reference is made to the basin- 

 range problem, showing that it was still borne in mind; on October 29, a diagram, here re- 

 produced, is labelled: "An attempt to sketch the Fish Spring-House Range to illustrate its 

 structure"; but that is all. The foreground member of the group presumably represents 

 the Confusion Range on the South. Unfortunately the excellent device of adding a vertical 

 section to the foreground, adopted a few years later by Holmes in his illustrations for Powell's 



