846 CS IETIOH) 
At many localities the Belt series is seen to be in conformable rela- 
tions to overlying fossiliferous rocks of Cambrian age, the Flathead 
and Gallatin formations, and, while assigned to the Algonkian, the 
series is spoken of as forming the lower part of the Paleozoic of the 
area. 
Comment.— It is unfortunate that rocks assigned to the Algonkian 
should be spoken of as forming the lower part of the Paleozoic, even 
though the Belt series may be a downward conformable extension of the 
Paleozoic. If properly Algonkian, z. ¢., sedimentaries and equivalent 
igneous rocks below the Olenellus horizon, whether conformable or 
not, if referred to any era, they should be referred to the Proterozoic. 
Weed and Pirsson* briefly describe the geology of the Little 
Rocky Mountains of central Montana. The core of the mountains is 
formed of crystalline schists, of which the type most usually seen is a 
black glistening amphibole-schist, or amphibolite. In the saddle 
west of Shellrock Mountain, the series consists of amphibole-schists 
and mica-schists, pink gneiss, and white quartzites, the various rocks 
occurring in rapidly alternating beds but a few feet thick. 
The crystalline schists are overlain by Cambrian sedimentaries. 
Intruded between the schists and sedimentaries is a great laccolithic 
body of granite-porphyry. 
The presence of the quartzite is taken as indicating the Algonkian 
age of the crystalline series. However, similar schists occurring in 
Montana have been generally classed as Archean, and these rocks are 
metamorphosed and quite unlike the slightly altered Belt Mountain 
Algonkianseries. ‘The crystallines are, therefore, not definitely assigned 
to either the Archean or Algonkian. 
Hague, Weed, and Iddings* map and describe the geology of the 
Yellowstone National Park, Wyoming. Archean rocks are found near 
the borders of the district in the mountain ranges which encircle the 
Park plateau. They comprise granites, gneisses, and schists. The 
granites and gneisses are for the most part coarsely crystalline, and 
the entire series shows the effect of metamorphism by pressure. 
Algonkian rocks are recognized only in the southern end of the 
t The geology of the Little Rocky Mountains, by W. H. WEED and L. V. Pirs- 
SON. Jour. GEOL., Vol. IV, 1896, pp. 399-428. 
2 Geol. Atlas of the United States, Yellowstone National Park Folio, No. 30, by 
ARNOLD Hacue, W. H. WEED, and J. P. Ippincs. Washington, 1896. 
