172 GEOLOGICAL SURVEY OF THE TERRITORIES. 



They are followed by very hard, compact, micaceous sandstones. During 

 the upheaval of this range, the line of force seems at first to have been 

 vertical, and tipped up the layers as we see them on the eastern side. 

 Then the force seems to have acted in a line oblique to its former direc- 

 tion, and, breaking through the Silurian and partialy through the Car- 

 boniferous layers, carried their lower edges to the westward ; so that, 

 while the Cretaceous, Jurassic, and a portion of the Carboniferous 

 layers dip in an easterly direction, the remainder of the Carboniferous 

 and all of the Silurian beds dip toward the west. This remarkable 

 occurrence is fully treated of in Dr. Hayden's report, in which there is 

 also a section showing the various beds. 



From Flat- Head Pass we crossed the country in a northwesterly di- 

 rection to the Missouri Eiver, striking it at Horse-Shoe Bend, below the 

 Three Forks. Between these two points there are a number of local 

 synclinals and anticliuals. From Horse Shoe Bend, we proceeded up 

 the Missouri Eiver to the junction of the Gallatin. About four miles 

 above Gallatin City there is a magnificent exposure of strata on the 

 east side of the river. The following section is in ascending order from 

 the lowest exposure to the Jurassic beds. 



Feet. 



1. Micaceous sandstones, iuterlaminated with blue, shaly lime- 



stones, weathering brownish, in bands, varying from a few 

 inches to a foot or more in thickness. The upper layers of 

 the sandstone are of a steel-gray color, breaking into cubical 

 blocks, that give it the appearance, from a distance, of basalt. 

 The general color of the sandstones is an olive-green. They 

 contain fine grains of mica and small pebbles of quartz, 

 mixed with a few opaque crystals of white feldspar. The 

 rock is very hard, and has been little affected by the weather. 

 It extends in high bluffs for considerable distance along the 

 river. Some of the limestones contain flat, rounded concre- 

 tions of about 6 inches in diameter and 3 inches in thickness. 

 The sandstones vary in thickness from 2 to 4 feet. The gene- 

 ral dip is northwest, inclination being 25° to 30°. The thick- 

 ness of these beds is about 1, 600 



2. Pink sandstones, above which are heavy beds of quartzite. 



The general dip is about 30° northwest. Thickness, esti- 

 mated at 100 



3. Green and blackish shales, breaking into lamina of a few inches 



thickness. Low down we find layers that are of a deep pur- 

 plish, red color. Short distance above these latter, we find a 

 very hard calcareous sandstone, containing grains of a mine- . 

 ral resembling glaueonite. In them we find also the remains 

 of trilobites. A short distance above this layer we find sand- 

 stones of about 3 inches thickness, iuterlaminated with green 

 argillaceous shales, containing trilobites, Idngulepis, Gono- 

 ceryplie, &g. The estimated thickness of these beds is 300 



4. Layers of very hard limestone, breaking into lamina of an 



inch or more in thickness and containing immense quantities 



of trilobites. Thickness 40 



5. Black, shaly limestones, containing a small lAngula, Acrovleta, 



and Obolella, followed by rather thin layers of very compact, 



blue limestone. Thickness 50 



6. Pebbly beds of limes fcone, containing trilobites, and Lingulepis. 



Thickness 60 



