The Geology of the Commander Islands. 



The Commander Islands (Behring, Copper and 2 small 

 Islands) belong to the type of continental Islands (they 

 are only partly vulcanic). They are separeted from the 

 Peninsula Kamtchatka by a strait of about 90 geograph. 

 miles. From the Aleutian Islands they are separated by 

 a depth of more than 1600 fathoms. They are situated 

 on the boundary of vulcanic activity of the two vulcanic 

 groups: the Japanese-Kurile, Kamtchatka and Aleutian 

 Islands. They owe their appearance to vulcanic activity, 

 which left deep traces. The geological age of the Islands 

 is a very young one. Sedimentary rocks are known as 

 follows: the tertiary — pliocene, but the more important 

 sediments are the post-pliocene and alluvial ones, which 

 are of very recent origin. Fossils are very insignificant 

 in consequence of the vulcanic activity — metamorphosing 

 the sedimentary layers into schistic layers. By the character of 

 the fossils one may conclude, that the layers are formed 

 through shallow water. Predominating are slates metamor- 

 phosed in various ways, sand stones, conglomerates of an im- 

 mense power. Feldspath basalt form vulcanic rocks, which 

 have broken the previous layers and destroyed their hori- 

 zontality. The strangest vulcanic activity was on Copper 

 Isl. Basaltic eruptions occurred more than once, which 

 may be concluded by its structure. The earliest eruptions 

 were considerably destro3 7 ed by the influence of atmos- 

 phere and water. Dislocations were more energetically 

 proved on Copper Isl., where one comes across a suite 

 of layers in an almost vertical position. The chain of 

 mountains on the Islands extend from Nord-West to South- 

 East. On Behring Island this chain is crossed by narrow 



