Septembee 17, 1915] 



SCIENCE 



377 



sent without danger of carrying plant diseases 

 or insect pests. 



Maude Kellerman 

 BuEEAU OF Plant Industey 



VALLEY-FILL OF ARID INTERMONT PLAINS 



Unfailing tendency too broadly to general- 

 ize from a new-found principle is nowhere 

 better shown than in the instance of ascribed 

 origin of the wide intennont plains of the 

 Great Basin in particular and in general of 

 all desert tracts of the globe. So graphic are 

 the descriptions of Basin Range features given 

 by the various members of the famous Fortieth 

 Parallel Survey that even after the elapse of 

 half a century they continue to hold first place 

 •with scarcely a question concerning the accu- 

 racy of their genetic foundation. 



One statement of the late Professor I. C. 

 Eussell furnishes the keynote to the whole 

 problem. He speaks of the mountains of 

 Nevada being " buried up to their shoulders 

 in the debris of their own substances." As a 

 corollary he ascribes enormous depths of 2,000 

 to 3,000 feet to the valley-fill between the vari- 

 ous basin ranges. Russell's observations, as 

 weU as those of others, are mainly impressions 

 gained on hurried reconnaissances through the 

 region; and the statements made at the time 

 leally had little to substantiate them. The 

 conceptions which they represent are in the 

 extreme brilliant and suggestive. For this 

 very reason it is that they go so long unchal- 

 lenged. 



Singularly enough one of Russell's most 

 typical examples of buried mountains, and one 

 oftenest cited as around which the valley-fill is 

 thickest, is a district whereiu subsequent in- 

 vestigation conclusively shows the valleys or 

 interment plains to have rock-floors. In these 

 valleys the strata of the bed-rock are flexed 

 and tilted often to a vertical attitude. The 

 planed surface coincides nearly with the pres- 

 ent ground surface. The wash or valley-fill is 

 almost nil. To be sure there may be some in- 

 stances in which there is a valley filling that 

 has greater or less depth; but in many cases 

 the broad interment basin has a very pro- 



nounced rock-fioor and the thickness of rego- 

 lith or soil mantle is inappreciable. 



Other critical data now exist that bear di- 

 rectly upon the extent of the valley-filling. 

 The larger number of deep drill-holes, which 

 have been put down in the desert regions of 

 the west during recent years, furnish some 

 very conclusive evidence touching the points 

 under consideration. Of course well-logs, as 

 a rule, are notoriously fanciful and, without 

 proper checks, can not be implicitly relied 

 upon. Yet many such records are adduced as 

 proving the great depth of vaUey-fillings. 



In a number of cases, which are really test- 

 cases, depths of 2,000 to 3,000 feet are reported 

 as being entirely in wash material. These 

 statements are even presented in scientific lit- 

 erature. In one instance, in which soft Eocene 

 clays and sands were dipping at an angle of 

 YO degrees, the drill is reported as having 

 penetrated nearly 2,500 feet of wash debris 

 without passing through it. In another case, 

 that of the Santa Cruz Valley, near Tucson, 

 Arizona, the valley-fill was said to be over 

 2,000 feet thick as shown by the driU; yet the 

 late W J McGee found bed-rock near-by cov- 

 ered only by a few inches of soU. 



One of the latest cases of this kind is the 

 interpretation of deep-drill records in the 

 Hueco (Tularosa) bolson in southern New 

 Mexico. Drill-logs of more than 2,000 feet 

 are given as evidence in support of the conten- 

 tion of the great depth of valley-fill. As a 

 matter of fact, and as the records themselves 

 clearly indicate, the beds passed through by 

 the drill are the very red-beds that overlie the 

 Carboniferous limestones of the region, and 

 that one would expect first to encounter a 

 short distance beneath the surface of the 

 desert at those points. Abundant other data 

 from this locality point rather conclusively to 

 the fact that this so-called valley-fiU is mainly 

 not wash debris at all but typical soft red- 

 beds. This seems to be another instance of 

 forcing facts to fit theory. 



What is stiU greatly needed in these desert 

 investigations is further critical evidence 

 bearing upon the geological date of the forma- 

 tion of the so-called Basin Range structures. 



