KELATIONSHIPS OF THE TERRAXES 201 



nizable clastic rocks. This base is easily recognized beneath the Belt 

 series of rocks in INIontana, in the Grand Canyon region of Arizona, in 

 portions of the T>ake Superior region, and in eastern Newfoundland, as 

 there are great unconformities between the Algonkian and the Archean, 

 above which the clastic rocks are clearly defined. In other regions, 

 however, the delimitation of the Algonkian and the Archean is very 

 dijfificult. The basal plain of the Algonkian is obscured by volcanic 

 rocks which, with the elastics, have been so altered and folded that it 

 is practically impossible to differentiate them from the fundamental 

 Archean complex. Frequently areas of rocks are met which can not 

 with certainty be placed either with the Algonkian or with the Archean. 

 The difficult}^ of defining in all areas the exact line of separation between 

 the Algonkian and the Archean is not peculiar to this horizon, as interme- 

 diate beds are to be found between the Algonkian and the Cambrian, 

 the Cambrian and the Ordovician, and so on. 



. Under the definition that all elastics older than the Cambrian are to be 

 included in the Algonkian, the rocks of the Belt terrane of Montana, 

 the Grand Canyon series of Arizona, the Llano series of Texas, and 

 the Avalon terrane of Newfoundland are all clearly Algonkian. 



Geological Notes 

 belt terrane 



Literature of the subject. — Dr F. V. Hayden first described, in 1860, the 

 strata now referred to the Belt terrane.* In his Fifth and Sixth An- 

 nual Reports of Progress t be refers the same formation to the Lower 

 Silurian as a portion of the " Potsdam " series, considering them an un- 

 conformable downward extension of the Paleozoic series. 



The Belt rocks were also described and partial sections given by Grin- 

 nell and Dana, in 1875, from the vicinity of Fort Logan and White 

 Sulphur Springs.! Later, when reporting the results of Dr A. C. Peale's 

 field work, Dr Hayden refers to the " East Gallatin group "'§ as a name 

 given by Dr Peale to the slates, saiidstones, and impure limestones 

 beneath the fossiliferous Cambrian rocks. Again, in the same connec- 

 tion, reference is made by him to the East Gallatin group as probably 

 middle Cambrian.] | 



♦Exploration of the Yellowstone and Missouri rivers, 1860, p. 91. 



t Preliminary Report U. S. Geol. Survey, Montana, 187-2, p. UU ; Sixth Ann. Report U. S. Geol. 

 Survey of the Territories, 1873, pp. 72, 73. 



t Reconnaissance from Carr-ill, Montana, to Yellowstone Park, U. S. War D^pt,, Washington, 

 1876, p. 116. 



g Sixth Ann. Report U. S. Geol. Survey, 188.5, p. .50. 



|] Seventh Ann. Report U, S, Geol. Survey, 1888, p. 86, 



