REVIEWS 6 1 



Igneous rocks occur sparingly in the Algonkian series. An intrusive sheet of diorite 

 is extensive in the upper limestone formation and an extrusive flow of diabase caps it. 



The Algonkian strata form a syncline whose axis trends west of north. South- 

 western dips vary from 5° to 30'^. Northeastern dips are generally 30° to 40°, and 

 locally approach or pass verticality. Minor flexures within the syncline are very broad 

 and low. The northeastern limit of the fold is an eroded margin; the southwestern 

 is an anticlinal axis whose western limb is in part eroded, in part thrown down by a 

 normal fault along North Fork Valley. Syncline and anticlines are closely related to 

 valley and ridge respectively, and this relation extends to heights of peaks. 



Along its eastern margin the oldest Algonkian formation rests upon Cretaceous 

 rocks. The outcrop of this abnormal contact is deeply sinuous throughout the stretch 

 from Saint Mary Lake to Waterton Lake. The structure is described as an over- 

 thrust fault, on which the Algonkian series has moved northeastward relatively over 

 the Cretaceous rocks. The displacement on the thrust surface is 7 miles or more, and the 

 vertical throw is estimated at 3,400 feet or more. The thrust surface dips from 0" to 10° 

 southwestward, and strikes variously from north to north 60° west. Thus it is warped, 

 and this warping is found to determine the general outline of the eastern face of the 

 Rocky Mountains, particularly the prominence of Chief Mountain, and the relative 

 position of the Lewis Range, en echelon to the Livingston. 



W. H. Weed. "Geology and Ore Deposits of the Elkhorn Mining District, 

 Jefferson County, Montana." Twenty -second Annual Report of the U. S. 

 Geological Survey, Part II, igoo-igoi, pp. 399-549. 



Weed describes and maps the geology of the Elkhorn mining district of Montana. 

 Doubtfully referred to the Algonkian are the Turnley hornstones. The lower division 

 is 200 feet thick and consists of shale metamorphosed to a very dense hornstone com- 

 posed of light brown biotite and quartz. A bed of impure iron ore 20 to 30 feet 

 thick occurs in the middle lower part of the formation. The quartzitic hornstones 

 overlie the basal beds just noted and are 200 feet thick. The rocks, though well 

 bedded, are very dense and hard, and are of a gray-black color, so that they closely 

 resemble the andesites. In color, composition, and relation to the overlying quartzite 

 the rocks correspond to the red Spokane shale of the Belt terrane seen at Whitehall, 

 20 miles south, at Townsend to the east, and at Helena on the north. 



W, S. Tangier Smith. "Geology of the Hartville Quadrangle of Wyom- 

 ing." Geologic Atlas of the U. S., Hartville Folio, No. 91, U. S. 

 Geological Survey, 1903, pp. 1-6. 



Smith ( W. S. Tangier) describes the geology of the Hartville quadrangle of 

 Wyoming. The Whalen group, assigned to the Algonkian, consists of gneisses, 

 schists, quartzites, and limestones, all very schistose, the schistosity standing nearly 

 vertical. These rocks occur principally in the northeastern part of the quadrangle. 

 Quartzites and micaceous schists form the greater part of the exposed rocks of the 

 Whalen group, and in places they grade into each other, so that no definite separation 

 can be made. Some of the quartzites are more or less calcareous. Iron ore occurs 

 within and near the contact of the limestones and schists of the Whalen group on the 

 west side of Whalen Canyon. Information at hand is not sufhcient to decide whether 

 there are several ore-bearing horizons or a single horizon repeated by folding. Ore 

 is being mined at Sunrise. 



