REPORT OF THE CHIEF ASTRONOMER 273 



SESSIONAL PAPER No. 25a 



bedding in schist or marble, as indicating the real stratigraphic relations in 

 any detail. A columnar section is as yet impossible. The brief description 

 of a few typical traverses may suffice to show the general characters of the rocks. 



Area East of Salmon River. — One of the most continuous exposures of the 

 group was found on the top of the broad ridge running westward from Lone 

 Star mountain. East of that peak the schist is in contact with the Lone Star 

 formation, but. as indicated above, the relation between the two formations is 

 very obscure. A special reason for the uncertainty as to the true relation is 

 found in the existence of the wide break in the section, caused by the intrusion 

 of the Lost Creek granite. 



From the bottom of the col between Beehive and Lone Star mountains 

 westward to the Salmon river, the dominant rock is a typical carbonaceous 

 phyllite. It is a very dark gray or greenish-gray to black rock, highly schistose, 

 and generally with few certain traces of 'the original bedding. For hundreds 

 of yards together along the ridge this greatly crumpled schist shows marked 

 homogeneity, but, in places, it passes into an abundant schistose, likewise car- 

 bonaceous quartzite. Both these phases may be calcareous and carry accessory 

 tremolite and epidote as metamorphic products, along with the quartz, sericite, 

 and carbon dust. The schists are often pyritized to some extent and in many 

 parts, bear numerous veins of mineralized quartz. Biotite is very often developed 

 as an abundant accessory constituent of the schists. Strain-slip schistosity 

 with the resulting crinkly rock-surface is well developed at many points. 



On the top of Lone Star mountain a pod of banded, white and bluish 

 marble is intercalated in the phyllite-quartzite. The limestone is enormously 

 crumpled and mashed, so that it is impossible to determine its thickness. Its 

 average dip seems to be 30° to the east. A mile west of Lone Star peak a 

 much larger intercalation of banded, dark gray and bluish-white marble crosses 

 the ridge. It can be followed continuously on a band of fairly constant width 

 from Lost creek to, and beyond, Sheep creek on the north. The continuity 

 suggests that this band represents a sedimentary member which retains nearly 

 its original thickness and has not been seriously thinned or thickened by 

 orogenic shearing. In this view the thickness must be at least 2,000 feet, for 

 the true dip is 70° and is against the mountain slope, while the width of the 

 band is nearly half a mile. 



This limestone, like all the others found in the area now described, is a 

 true marble, fine-grained and completely recrystallized. None of the limestones 

 of the group seems to be magnesian to any great extent; all the specimens col- 

 lected effervesce violently with cold, dilute acid. Occasionally flattened grains 

 of quartz appear in thin sections and, more rarely, minute crystals of basic 

 plagioclase, probably anorthite, lie scattered through the thin section. Chert 

 nodules or beds were never seen in any of the marbles. In one bed on the south 

 side of Salmon river, concretions of finely granular quartz of the size of 

 large peas, are embedded in calcite. Excepting these accidental ingredients 

 the marbles are to be regarded as composed of notably pure cerium carbonate. 

 25a — vol. ii — 18 



