SUMMARY 27 



limestone is rarely found west of the Mission range, although the 

 siliceous sediments are very fine, often indicating the deposition of 

 siliceous mud rather than sands. 



The great source of sediments, as suggested by Doctor Daly, must 

 have been to the west and northwest of the Kootenay valley. A more or 

 less shallow open sea extended eastward 300 miles or more. In the 

 vicinity of Neihart, Montana, there is a trace of the eastern shoreline in 

 the uplift of Archean gneiss and schist, with the basal conglomerate 

 resting upon it. Occasional beds of conglomerate also occur in higher 

 formations of the Algonkian 20 miles and more away from the Neihart 

 Archean. It seems probable that the latter exposure is of an area that 

 was soon buried by the Algonkian sediments, and that the main eastern 

 shoreline, or land area, was still farther eastward during most of Algon- 

 kian time. From the character of the Algonkian sediments of the Little 

 Belt mountains it also appears that the eastern land area afforded very 

 little coarse material. It may have been low, sending only muds and 

 solutions of lime and silica to the Algonkian sea, along with an occasional 

 rush of sand and fine gravels. 



Summary 



The Algonkian rocks which form the subject of this paper represent a 

 total thickness of 37,000 feet and occupy an area extending from the 

 Little Belt mountains on the southeast to the vicinity of Cceur d'Alene 

 on the west and northward into British Columbia. The Camp Creek, 

 Mission Eange section occurs near the center of this area and is taken 

 as the type because of its great vertical extent (24,770 feet) and the fact 

 that it is capped by Cambrian strata. 



In the four sections measured by the writer the Algonkian or Belt ter- 

 rane is overlain unconformably by massive, coarse grained sandstones 

 referred to the Middle Cambrian. The unconformity is usually indi- 

 cated by great changes in the volume of the underlying strata and repre- 

 sents a considerable time interval. From the presence of Lower Cam- 

 brian fossils in the Bow Eiver series of McConnell it is believed that this 

 series was laid down during the erosion interval between the Algonkian 

 and the Middle Cambrian in Montana. 



The physical conditions under which the Belt terrane was deposited 

 are very clearly indicated by the change in the character of sediment- 

 ation from the conglomerates, grits, and coarse sandstones on the north- 

 west to the limestones, fine sandstones, and shales on the southeast. The 

 land area from which these sediments were mainly derived must have 



