228 IDET JOLIN AIL WF (CIS OIL OG VY. 
physical and mechanical facts seem to show that the fissures of this 
complex were filled by fine quicksand, injected from an unknown 
source, containing a large amount of homogeneous material. 
Peale* places the Belt formation of the Three Forks sheet in the 
Algonkian. This formation at the East Gallitan River is 2300 feet 
thick and consists of an alternation of coarse, micaceous sandstones and 
conglomerates, with beds of hard argillaceous slates, and bands of thin- 
bedded, dark blue, siliceous limestones. ‘The latter are very hard and 
some are slightly magnesian. The lhmestones occur mainly towards 
the base of the section, in bands ordinarily from five to twenty feet in 
thickness, but sometimes reaching nearly fifty feet. On the Bridger 
range the formation has a thickness of at least 6000 feet. It is also 
characteristically exposed in the Canon of Jefferson River fourteen or 
fifteen miles above its mouth. 
Nowhere in the Gallitan valley is the belt formation found in 
immediate superposition upon the Archean, but that it is post-Archean 
is shown by its being made up largely of Archean débris. Between the 
Belt formation and the overlying Flat Head Cambrian quartzite there 
is no well defined unconformity, although there was an important oro- 
graphic movement between the two, the entire area of the Three Forks 
sheet being submerged at this time. Little, if any, induration is seen 
in the Flathead formation, while the Belt beds are so altered in most 
cases as to resemble closely the metamorphic crystalline rocks which 
underlie them, and from which they were derived by their breaking 
down. Notwithstanding the metamorphism there is no mistaking the 
sedimentary character of the Belt formation. 
We have, therefore, a non-fossiliferous formation of clastic beds, in 
some places highly metamorphosed, which lies between the Archean 
gneisses and a belt of quartzite, above which are beds with Middle 
Cambrian fossils. From its stratigraphical position this formation can 
be only of Lower Cambrian or of Algonkian age. 
The possibility that Lower Cambrian fossils may yet be found in 
the quartzite at the base of the Flathead formation; the absence of 
organic remains in the Belt formation ; the metamorphosed condition 
of the latter, and the existence of an orographic movement between 
the quartzite and the beds below lead us to refer the latter, for the 
present at least, to the Algonkian. 
*The Paleozoic Section in the Vicinity of Three Forks, Montana, by A. C. PEALE. 
Bull. 110, U. S. G. S., 1893, pp. 56. 
