THE ARCHEOZOIC ERA. 



153 



Some members of the series are clearly intrusive in others, and therefore younger. 

 The older members show profound metamorphism. In the older formations a 

 first dynamic movement developed foliation in rocks which were originally 

 igneous, while a second folded the planes of foliation. Two profound meta- 

 morphic movements are thus recorded. 



The Archean of the great western belt has similar characters. In the Grand 

 Canyon of the Colorado, in northern Arizona, the same types of rock (the Vishnu 

 terrane l ) are exposed. They are separated from the Cambrian by the Grand 

 Canyon system, 2 itself divisible into two series by an unconformity, 3 the upper 

 being unconformable below the Cambrian. 



The relations of the Archean at various other points in the west are 

 illustrated by Figs. 45 to 48. 



The structure of the Archean system is usually more complex than 

 would be inferred from any brief descriptions, such as those given 



Fig. 45. — Section showing the relations of the Archean to other formations near Fort 

 Benton, Montana. Atgn, Archean gneiss; €\ Cambrian; D, Devonian; C, Car- 

 boniferous; J, Jurassic; K, Cretaceous; bp, Barker porphvrv. Length of section, 

 about 21 miles. (Weed, U. S. Geol. Surv.) 



above. It would indeed be difficult to obtain an exaggerated idea 

 of the complexity of the relations of the various sorts of rock which 



Fig. 46. — Section showing the relation of Archean to younger formations near Liv- 

 ingston, Montana. JR, Archean; C, Cambrian (Gallatin limestone); I), De- 

 vonian (Three Forks shale and Jefferson limestone); C, Carboniferous (Madison 

 limestone and Quadrant quartzite); J, Jurassic (Ellis formation); Kd, Kc, Km, 

 Kl, and Klv, Cretaceous (Dakota, Colorado, Montana, Laramie, and Livingston, 

 respectively). Length of section, 11 miles. (Weed, U. S. Geol. Surv.) 



have caused this system to be called variously the "Archean com- 

 plex," the " basement complex," the "fundamental complex," etc. 



1 Van Hise, Bull. 86, IT. S. Geol. Surv.; and Walcott, 14th Ann. Rept., U. S. Geol. 

 Surv., Pt. II, p. 506. 



2 Powell, U. S. Geol. Surv., and Geog. Surv. of the Territories; Rept. on the Geology 

 of the Eastern Portion of the Uinta Mountains, 1876, p. 70. 



3 Walcott, 14th Ann. Rept. IT. S. Geol. Surv., Pt. II, p. 506. The Vishnu of Wal- 

 cott appears to be Archean, leaving only the Unkar and the Chuar divisions of the 

 Grand Canyon series between the Archean and the Cambrian. 



