844 (On IK ML JBI ILE 
rivers in the Rocky Mountains of western Canada. The Archean’ 
rocks of the district consist of a series of well foliated mica-gneisses, 
mica-schists, hornblende- and actinolite-schists, quartzose schists, and 
crystalline limestones. ‘The rocks of the series are usually evenly 
bedded, and conform in dip to the overlying formations. To the 
series the local term Shuswap is applied. 
Shuswap rocks are found on both sides of the Finlay River, from 
its mouth up to its junction with the Ingenica. North of this point 
the formation divides. ‘The eastern limb follows the eastern slope of 
the Finlay valley northwestward to the Quadacha and for some dis- 
tance beyond. It has a width of four miles at Paul’s Branch, where it 
forms the most westerly range of the Rocky Mountains. ‘This width 
decreases towards the north and increases to the south. The western 
limb bends away from the Finlay above the Ingenica, but crosses it 
again at the great bend which the Finlay describes after leaving the 
Rocky Mountains, and continues on to the north. The width of this 
band was not ascertained, as its western boundary was not reached. 
Another area of Shuswap rocks, separated from the first by a band 
of limestones, occurs on the Omenica River above the Oslinca. ‘The 
band has a width of ten miles. 
The Shuswap series is overlain by Lower Paleozoic strata. 
Peale? maps and describes the geology of the Three Forks quad- 
rangle of Montana. Archean gneisses and Algonkian sediments 
occupy large areas. The Archean gneisses occur principally in the 
foothills of the Bridger range, the mountain masses at the northern 
and southern ends of the Madison range, west of the Madison valley 
and north of Virginia City, the southern part of the Jefferson range, 
the foothills of the Gallatin range, south of the Gallatin valley, and 
beneath the Bozeman Lake beds at the southern end of the plateau, 
between the Gallatin and Madison valleys. The rocks referred to the 
Archean may possibly include some that eventually may be referred to 
the Algonkian. The contacts of the Archean with the overlying sedi- 
mentaries are, in all cases, unconformable. 
The Algonkian series comprises two divisions, the Cherry Creek 
beds, and the Belt formation. 
tIn conformity with the usage of Canadian geologists, Archean is above used in 
the sense of pre-Cambrian. 
Geol. Atlas of the United States, Three Forks Folio, No. 24, by A. C. PEALE. 
Washington, 1896. 
