Reviews 



Eocene Glacial Deposits of Southwestern Colorado. By Wallace 

 W. Atwood. Prof. Paper, U.S. Geol. Surv., No. 95-B, 1915. 

 Pp. 13-26, pis. 4, figs. 11. 



Glacial deposits of Eocene age were discovered in 1913 near Ridg- 

 way, Colorado, northwest of the San Juan Mountains. The nine 

 exposures are scattered over an area of 20 square miles. The Ridgway 

 till rests on the Mancos shale and is overlain by the Telluride con- 

 glomerate and San Juan tuff. The till is divided into two members. 

 The lower is a bowlder till containing many striated stones, some very 

 large. The upper till is a dark slate-colored clay, unstratified and 

 containing only a few striated pebbles. The bowlder till is believed to 

 have been deposited by glaciers heading in the region of the present 

 San Juans. The pebble till may have been deposited by ice moving 

 over extensive surface exposures of Mancos shale from the region of 

 the West Elk Mountains to the northeast. 



The paper closes with a summary of the distribution of pre- 

 Pleistocene glaciation. An extensive bibliography is appended. 



H. R. B. 



The Yentna District, Alaska. By Stephen R. Capps. U.S. 

 Geol. Surv., Bull. No. 534, 1913. Pp. 75, pis. 13, figs. 7. 



This area lies along the southeast base of the Alaska Range in the 

 drainage basin of the Yentna River, a tributary of the Susitna. The 

 oldest rocks are a pre- Jurassic series of slates and graywackes. They 

 are everywhere faulted and folded, and are intruded by igneous rocks 

 ranging from granite to diorite. The intrusives are provisionally 

 assigned to the late Lower Jurassic or Middle Jurassic. Older dikes 

 of diabase and greenstone have been deformed and metamorphosed 

 along with the slate series. 



Next younger are rocks of Eocene age, consisting of sands, shales, 

 gravels, and commonly some lignitic coal. Coarse stream gravels 

 overlie the coal-bearing series. Evidence of the Tertiary age of the 

 gravels was obtained. They were formerly regarded as Pleistocene. 



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