602 



REPORT OF NATIONAL MUSEUM, 1904. 



Fiff.l 



Serf ion skowinff probable method of intrusion of masses 

 of* trachyte . 



In the season of 1876 C. A. White was at work in northwest Colo- 

 rado, including 1 the area lying between the Uinta and Park ranges. 

 F. M. Endlich was engaged in the survey of the White River district, 

 A. C. Peale of the Grand River district, and W. H. Holmes of the 

 Sierra Abajo and West Miguel mountains. 



In the interval between the issue of the reports for 1875 and 1876 

 Hayden, at the suggestion of King, had decided to call the transition 

 group, heretofore referred to by him as Lignitic and the exact geolog- 

 ical position of which was still in dispute, the Laramie group. 



The report of this year contained little that is new or striking, the 



^ work resulting mainly in 



an extension of our knowl- 

 edge of the geographic 

 range of various geological 

 formations. White, work- 

 ing in the Uinta region, 

 aptly compared the struc- 

 ture of Junction Mountain 

 to a displacement which 

 might be illustrated by the 

 action of a large punch 

 worked by machinery, the 

 perforated heavy iron 

 plates being somewhat 

 torn in places and nowhere 

 clearly cut through in the 

 process of punching. The 

 work of White this year 

 as a whole confirmed the 

 view held by Hayden that 

 these lignitic or Laramie 

 beds, as they are now 

 called, are of a transitional 

 nature. 



The field work for Colo- 

 rado was completed in 1876. The following year (1877) the work was 

 extended northward into Idaho and Wyoming. The geological work 

 was, as before, assigned to Drs. F. M. Endlich and A. C. Peale, with 

 the addition of Orestes St. John. Endlich worked in 



Work of Hayden in . . „ , . ,, n -r, . , . 



Idaho and the Sweetwater region, Peale in the Green River dis- 



Wyoming, 1877. . , _., _ ' . ,. „, . -.. . . . 



trict, and St. John in the leton district. 

 S. H. Scudder spent two months of the year in Colorado, Wyom- 

 ing, and Utah in collecting fossil insects, which were subsequently 

 described in the thirteenth monograph of this survey. Sir Joseph 

 Hooker, director of the Kew Gardens, England, and Prof. Asa (nay. 



china oP strata produced by intrusion of single 

 distributed. 



Fl?.3. 

 //egrce of arching really produced by Hie irregular 



Intrusion of'tnasse.s of Trachyte- 

 Sierra el Late. 



Fig. 107. — Sections across the Sierra el Late. 

 Holmes.) 



(After W. H. 



