26 GEOLOGICAL SURVEY OF* THE TERRITORIES. 



somber, apparently ba.saltic rocks, which, except for their structure aud 

 coh)r, I would rei^ard as Cretaceous or Tertiary. The whole series is 

 arranged in beds of marl, with more or less compact layers of harder rock, 

 which project out the same as in those formations. In these upper beds 

 I found fragments of wood, and in the ui)perjn()st beds were fragments of 

 leaves, which I cannot but regard as of Tertiary age, aud that the whole 

 series of beds have been greatly affected by heat so that the lowest beds 

 have been entirely chauged. Passing up the mountain we found our- 

 selves in a synclinal basin, witli the strata dipi)ing at a low angle, those 

 at the southeast at an angle varying from 30° to 00°, apparently com- 

 l)rising the diiferent formatious from Tertiary to Carboniferous. The 

 rocks do not show so many signs of heat as heretofore. Our course has 

 been directly north, and mostly through Carboniferous rocks, dipping 

 about southeast at an angle of -!U°. There are, in the cahon that we passed 

 through, at least 1,000 feet of limestone exposed, and as we leave the 

 canon northward we find 200 to 300 feet of red marly limestones, much 

 like the red deposits we have before met with, only harder. These rocks 

 are peculiar, differing from any before seen. They pass from a red loose 

 slate down into a compact clay-slate, gradually varying from a deep red 

 to black thin slates, becoming more and more compact as we descen<l, 

 until they appear to be a melted rock, and the joints are so close that 

 they separate the wliole mass into small fragments. The rock does not 

 eflervesce at all with sulphuric acid, but is of a very compact texture. 

 In regard to the age of these beds 1 can form no exact idea, no fossils 

 haviug been detected, though frequent sun-cracks are seen upon the 

 surface of the slates." 



The following i)aragraph, describing one of the four passes near 

 Henry's Lake, is taken from the re]Jort of Colonel W. F. Eayuolds of 

 his explorations in 1800, page 98 : 



"The ]xiss is only four miles from, and 200 feet above, the lake, and 

 so level that it is difficult to locate the exact point at which the waters 

 divide. It is about a mile in width, with the sides sloping gently to the 

 center. • The barometer stood at 23.05 inches, indicating a height of 

 C,350 feet above the sea-level, or 1,500 feet lower than the summit of the 

 South Pass. The approaches upon either side are remai kable, being of 

 about a uniform ascent of 50 feet to the mile, and thus afibrding un- 

 equaled facilities for either wagon-road or railroad puri)Oses. I luimed 

 it Low Pass, and deem it to be one of the most remarkable and 

 important features of the topography of the Pocky Mountains." 



This beautiful ])ass has been so carefully described by Colonel Pey- 

 nolds that I gladly record its name on an ofhcial map asPeynolds'sPass; 

 the name Low Pass, given it by Colonel Peyuolds, not being sufficiently 

 distinctive for a geographical name. 



CHAPTEll 11. 

 GALLATIN VALLEY— YELLOWSTONE VALLEY. 



In my annual report for 1871 I gave a brief description of the Gallatin 

 Valley ; but inasmilch as one division of the survey took Foit Ellis as 

 its initial point again in 1872, I shall reiuler the ])resent account more 

 clear by presenting a resume of the geology of the \alley. 



In beauty and fertility the valley of the Gallatin surpasses all others 



