PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 183 
of the Selkirk Mountain system in parallel bands striking about 
north 15° east. 
The succession overlying the Priest River terrane is sedimen- 
tary with the exception of an extensive basal lava flow, the Purcell 
lava which occurs in the eastern portion. The extent of the latter 
makes it a good horizon marker. Geographically, this succession 
is classified from west to east as the Summit, Purcell, Galton, and 
Lewis series. The Summit series of the Selkirks is the only one 
whose base is exposed. It unconformably overlies the Priest River 
terrane. The various members of these series are correlated with 
reference to their position above or below the Purcell lava, their 
mineralogical constituents, and general lithological characteris- 
tics, special emphasis being laid upon the molar tooth structure of 
certain carbonate formations due to the weathering of a peculiar 
mixture of dolomite and limestone, the presence of a certain ortho- 
clase feldspar with a characteristic microperthitic intergrowth, 
the presence or absence of red iron oxide, etc. In the Selkirks the 
sediments are chiefly clastic, conglomerates being important at the 
base. To the eastward, these grade into finer-grained clastics and 
carbonate. The easternmost part of the series is composed domi- 
nantly of carbonates. Red color is also more prominent in the 
more easterly series especially in their upper portions. 
The only fossils found are the species Beltina danaz which occur 
in the Altyn limestone in the lower portion of the Lewis series. 
This limestone and the one underlying it are classed as Beltian. 
The Beltian and Cambrian beds are bent into open nearly 
north and south trending folds which are disturbed by normal 
faults, most of which trend in the same direction as the folds. The 
Lewis series has been pushed over the Mesozoic sediments of the 
Great Plains along a thrust fault dipping westward at a low 
angle. 
In the case of the Lewis series, the Altyn dolomite and the 
Waterton dolomite below it are referred to the Beltian because of 
the presence of Beltina danai in the Altyn. The basis for the 
separation of the series into Beltian and Cambrian is not so appar- 
ent. The correlation of the beds designated as Cambrian is based 
chiefly on the lithological similarity of the Siyeh limestone with the 
