SODA BUTTE VALLEY. 213 



The foregoing' section was observed on the north side of Soda Butte 

 Creek, near the forty-fifth meridian, the locality being a mile west of that 

 just noted. Mottled limestones form the lowest strata exposed, occurring 

 100 feet above, an exposure of quartz-porphyry. The lowest bed is a fissile, 

 dark-colored limestone, carrying numerous fragments of trilobites and over- 

 lain by a massive, dark-colored, mottled limestone, which is the base of the 

 Gallatin formation, and which here forms a cliff fully 100 feet high. This 

 is the lowest horizon seen on the north side of the creek, but on the south 

 there are patches of shale which belong to the Flathead formation. Above 

 the dark, coarsely mottled limestone cliffs are more thinly bedded, gray 

 limestones and limestone conglomerates. Fossils collected from this hori- 

 zon are of Cambrian age and were obtained 60 feet above the top of the 

 cliff. At 1,050 feet above the stream similar limestones form projecting 

 ledges, and the rock carries many trilobite spines and a few fossils. The 

 rocks 50 feet higher up are similar and carry similar fossils and a few cri- 

 noid stems, which in this region are not commonly found at this horizon. 

 A heavy belt of light-gray limestone, weathering with a rough surface and 

 showing no fossils except crinoid stems, and representing, it is believed, the 

 Jefferson formation, occurs at 1,150 feet above the stream. This belt is 

 about 200 feet thick and is overlain by a white, much brecciated limestone 

 about 20 feet thick, overlain in turn by gray limestones 5 to 10 feet thick, 

 carrying traces of fossils and some chert. These limestone beds are nearly 

 horizontal, although at the west end of the low saddle between Pebble 

 Creek and the Soda Butte Valley they dip 30° SW. This sudden change 

 in dip is probably due to intrusive quartz-porphyry that may form a 

 laccolithic mass under the horizontal beds that occur at the highest point, 

 Section of beds at north base of Abiathar Peak. 



Feet. 



i' Andesitic breccia, forming summit of mountain. 

 Limestones, carrying Carboniferous fossils 150 

 Massive belt of indurated, gray limestone in which no fossils were found 175 



Beds generally covered by talus from the cliff above. At the base the ledges are 

 fossiliferous and carry an abuudance of shell remains, which are of Devonian 

 types. The rock is a fine-grained bnff or yellow limestone, varying to abrown- 

 1 gray limestone, very finely crystalline and carrying an abundance of finely stri- 

 ated shells 200 



[ Purplish and red limestones, thinly bedded and carry iug gastropod remains 20 



' Brown, earthy, and argillaceous limestone conglomerates 



Light and dark colored, thinly bedded limestones J. 200 



Three Forks. 



Jefferson . 



1 Crackled whito limestones 

 I Mas 



assive bed of light-colored limestone, forming peisistent cliff 200 



