Geology and Natural History. 83 



Resources of the Mount Wrangell District, Alaska." With the 

 paper are also published reconnaissance maps of the Copper 

 River region. 



The rocks of this district range in age from the earliest Pale- 

 ozoic down to the Pleistocene. The oldest rocks are metamor- 

 phosed sedimentaries including schists, slates, conglomerates and 

 feldspathic sandstones. The Carboniferous period is represented 

 by a large amount of volcanic rocks both as flows and as beds 

 of fragmental material. During the Permian marine conditions 

 prevailed and heavy white limestones and fossiliferous black 

 shales were formed. The study of the fossils in these rocks show 

 that these beds are allied with the Asiatic Indian beds rather 

 than with the eastern North American Permian. Sedimentation 

 in a gradual^ shoaling sea continued into the Triassic, at the end 

 of which time the previously formed rocks were folded and 

 elevated. Erosion followed and finally another period of sedi- 

 mentation occurred in Jura-Cretaceous time, during which coarse 

 conglomerates were laid down. With the close of the lower 

 Cretaceous this part of the continent became a land mass and has 

 remained so ever since. During Tertiary time considerable 

 movement took place accompanied by the effusion of hundreds of 

 cubic miles of Wrangell lavas, usually of andesitic type, and 

 causing the formation of the great central mountain group of the 

 region. Pleistocene silts, clays and gravels are found in the val- 

 leys. 



Copper is likely to prove the most important metalliferous 

 deposit of the area. The copper deposits are found in the foot- 

 hills to the south of the Wrangell Mountains and are everywhere 

 associated with an altered igneous rock called the Nikolai 

 greenstone. It is believed that the copper was originally dissem- 

 inated in minute quantities throughout this formation and that 

 the valuable dej)osits represent the concentration of this mate- 

 rial. The richer ore bodies generally lie in the upper part of the 

 greenstone near its contact with an overlying limestone. The 

 deposits may be divided into two classes ; tabular deposits which 

 are continuous for some distance and "bunch" deposits which 

 are irregular in shape and distribution. 



Gold has only been found in placer deposits, the most import- 

 ant district being the Chistochina field which covers a small area 

 in the northwestern part of the Copper River basin. The yield 

 from this district from its discovery in 1900 to the end of 1902 is 

 estimated as about $365,000. w. e. f. 



3. Geology of the Touapah Mining District, Nevada; by 

 Josiah Edward Sptjrr. U. S. G. S. Professional Paper No. 42. 

 278 pp., 14 pis., 78 figures in text. — This recent publication is a 

 timely description of a new and rapidly developing silver district 

 of western Nevada. The ore deposits of Tonapah were first discov- 

 ered in the spring of 1900 and before the end of the first year of 

 work had produced ore with a value of several million dollars. 



