Hanna — Notes on Pribilof Islands. 217 



with included crystals of yellow feldspathic minerals. 

 At one point on St. George Island the lava is built up to 

 an elevation of 1012 feet. Some large cones, however, 

 as Polovina on St. Paul, are composed almost exclusively 

 of red and black scorias. 



The evidence is conclusive therefore that violent vol- 

 canic action has built the islands as they exist to-day and 

 that all traces of these disturbances disappeared before 

 the advent of man. Casual inspection would lead one to 

 believe they were built from the ocean floor but there are 

 several points where a true conception of the geological 

 formation can be had. One of the best of these is at 

 Tolstoi Point, St. George Island. Here massive jasper 1 

 with grains and seams of quartz extends about 100 feet 

 above the sea, It it without stratification. The same 

 rock occurs above sea-level at Garden Cove, St. George 

 Island, and that it comes near the surface at several other 

 places on the islands is shown by the numerous pebbles 

 and bowlders of this material on the beaches. 



This massive jasper formed land masses at the Pribilof 

 Islands before the volcanic action which built the forms 

 which now exist. This is shown conclusively at Tolstoi 

 Point, St. George Island, by the layer of sand rock which 

 lies immediately above. This contains large quantities 

 of water-worn bowlders and pebbles, water-worn shells, 

 etc. It varies in thickness from two to ten feet and is 

 also found at Sea Lion Eookery, Garden Cove (St. George 

 Island), Ardiguen Rookery, Tolstoi Point, and Zapadni 

 Point (St. Paul Island). At some of these places the 

 sand rock does not extend high enough to expose the 

 underlying strata but near the top of each exposure there 

 are similar beach formations. 



Immediately on top of the sand rocks there are thick 

 beds of lava. The entire surface of all the elevated group 

 as it stands to-day is covered with this (and scoria), so 

 that any animals or plants which may have existed on the 

 previous land masses must have been wiped out. The 

 highest point which this former beach line (covered with 

 lava) reaches above the sea at the present time is about 

 100 feet so that it may be safely inferred this represents 

 the total amount of elevation of the ocean floor during the 

 volcanic period. 



1 The identifications of the minerals as given herein were made in the 

 Division of Geology, U. S. National Museum, under the direction of Dr. 

 George P. Merrill. 



