abstracts: geology 85 



irregular stockworks. The veins are up to 15 feet wide, but the average 

 is 5 feet. The stockworks are up to 80 feet wide, averaging from $3 to 

 $5 a ton in gold, and constitute the principal deposits. The gangue 

 material of the ores is quartz with subordinate calcite, and the principal 

 sulphide is pyrite with which are subordinate chalcoyprite, galena, and 

 sphalerite. Free gold is rarely seen. 



The wall rock of the ore bodies has been affected by locally intense 

 hydrothermal metamorphism, characterized by the development of 

 albite in small veinlets. This metamorphism is similar to that which 

 has transformed the Treadwell albite-diorite dike into an auriferous lode. 

 The ores are therefore of deep-seated and probably of magmatic origin. 



The diorite rocks of the Berners Bay and Juneau regions are part 

 of the great chain of batholithic Mesozoic intrusions that extends from 

 the Sierra Nevada of California northward into Alaska. Here, as in 

 California, the ascent of these magmas was accompanied by metalliza- 

 tion of great economic importance. A. K. 



GEOLOGY.- — Geology and mineral resources of parts of the Alaska 

 Peninsula. Wallace W. Atwood. Bulletin U. S. Geological 

 Survey No. 467. Pp. 137, with maps, sections, and views. 1911. 



The Aleutian Range forms the axis of the Alaska Peninsula, which 

 is the land mass separating the northern Pacific from Bering Sea. On 

 the Pacific side the mountains lie close to the sea, and the shore line is 

 broken by numerous embayments; on the Bering Sea side they are 

 separated from tidewater by a coastal plain which is notched by several 

 shallow bays and lagoons. 



The geologic history of the Alaska Peninsula, so far as it has been deter- 

 mined, is limited to Mesozoic and Cenozoic times. Some granitic rocks 

 in the northwestern portion of the province are known to be of pre-Upper 

 Jurassic age, but no rocks on the peninsula are definitely known to be 

 pre-Triassic. Since the opening of Mesozoic time sedimentation has 

 been going on in some portion of the peninsula during each of the great 

 geologic epochs, with the possible exception of the Pliocene and Oligo- 

 cene. The Triassic is represented in at least one locality. Large areas 

 of Jurassic sediments represent at least portions of the Middle Jurassic 

 and the Upper Jurassic series. The Lower Cretaceous and the Upper 

 Cretaceous are also present. There are also Eocene, possibly some Oli- 

 gocene, and certainly some Miocene sediments in the province. From 

 the Eocene epoch to the present time there have been numerous volcanic 

 outbursts at various places on the peninsula, and a portion of the mate- 

 rial ejected from the volcanoes is possibly of Pliocene age. The Pleisto- 



