Reviews 



Geology of the Hanagita-Bremner Region of Alaska. By F. H. 

 Moffit. U.S. Geol. Survey, Bull. No. 576. Pp. 55, figs. 6, 

 pis. 6, maps 2. 



The area described in this report is in the southern part of the Copper 

 River drainage basin. Chitina River bounds it on the north, and it 

 extends southward half-way to the coast. 



Field work in this region was of a reconnaissance character, but the 

 larger stratigraphic units have been outlined. The oldest sediments 

 are mainly schists, slates, and limestones, and have been referred to the 

 Carboniferous. These beds have been deformed by close folding and 

 faulting and cut locally by intrusions. Unconformable above them is 

 a series of interstratified beds of slate and graywacke thought to be 

 equivalent to the Valdez series, and early Mesozoic in age. This series 

 is in turn unconformable beneath conglomerates and tuffaceous slates 

 of Middle Jurassic age. 



The district presents a number of problems in physiography. The 

 drainage has a rectilinear arrangement which must bear some close rela- 

 tion to geologic structure. All the valleys have been profoundly glaci- 

 ated. Many streams are now eroding valley trains. A number of 

 situations appear very favorable for stream capture. 



The author is inclined to doubt the theory that Copper River is an 

 antecedent stream across the Chucagh Mountains. He suggests that 

 ice erosion over a narrow divide enabled a southward-flowing stream to 

 tap the Copper River and divert it from a westward course. To com- 

 plete this theory it seems necessary to assume uplift along the western 

 part of the basin to check the flow in that direction, and that along a 

 great part of its course the Copper River has been reversed since the 

 retreat of the ice. yj -g yy 



The Shinumo Quadrangle. By L. F. Noble. U.S. Geol. Survey, 



Bull. No. 549. Pp. 100, fig. 1, pis. 18. 



The remarkable geologic section exposed in the Shinumo quadrangle 



rivals those that have been described previously in the Grand Canyon. 



The generally unaltered condition of the beds, the great vertical extent 



