I ) 



J. STANLEY-BROWN — THE PRIBILOF ISLANDS. 407 



tiuns until overcome by the cooling waters of the ocean. This flow of highly 

 vesicular basalt, rich in Olivine, can be seen at many points on the shore. It forms 

 the floor of the island, and where not covered by overlying material its tongue-like 

 prolongations make reefs dangerous to navigation. Upon this basaltic pavement 

 were built up meanwhile the vents and cones, which now stand as perfect as on 

 the day of their completion. 



The third step in the process of construction was a second discharge of lava from 

 the central crater^ aided by feebler outpours from the vents which surround it. 

 This constitutes the overlying sheet. It is readily distinguished macroscopically 

 from the basement lava ; it is identical with it in mineralogic composition, but it is 

 more highly crystalline, and structurally it is pumiceous or spongy in texture rather 

 than vesicular. The contact of the two sheets is clearly marked and is invariably 

 near the water level. This latter fact is not due to wave action, for the markings 

 I: flowing lava remain on the basement surface at the line of contact, In this 

 upbuilding process perfectly arched volcanic tunnels with thin domes were formed 

 by the molten streams, while over the surface of the flow many jets of lava were 

 cooled and fractured into natural cairns so like the artificial monuments or " miaks " 

 made by the natives as to be readily mistaken for them. EUwould be difficult to 

 liud more trustworthy registers of orographic changes than these tall, tapering 

 cairns. 



The central portion of the island is today just as it was created: The lavas lie 

 unchanged in form and unaltered in their mineralogic constituents; no general 

 shifting of level has occurred to disturb the uprightness of the slender miaks, to 

 break down the fragile domes of the volcanic tunnels, or-to interfere with the hori- 

 zontally of the basement lava. On the southern shore an old sea beach of rounded 

 pebbles and bowlders made of fragments of the floor basalt now stands 25 or 30 feet 

 above the sea level, but the area involved would be represented only by a circle a 

 quarter of a mile across Thi' disturbance was local and due to the formation of a 

 small cone, only a few vestiges of which have been left by the sea. No glaciation 

 has smoothed away the cairns, carved the surfaces of the huge basaltic blocks, or 

 rounded their jagged edges. The cones and vents, which often bear tiny lakelets 

 in the cup-shaped depressions on their summits, stand unimpaired in their syin- 

 metry. In no place has erosion left a scar. No erratics are found on the higher 

 levels, except such pebblesas were brought by a novel geologic agent — the stomachs 

 of seals and sea lions. 



Every scrap of physical ami petrographic evidence indicates the recency of the 



island's formation, and a sea-dissected cone, known as Black bluff, on its eastern 

 side furnishes additional testimony. Distributed through this cliff of basaltic tuff 



arc rounded calcareous clay fragments, bearing fossil shells.* Extinct forms of 



it is stated by Elliot! in "Our Arctic Provii " (p 22!)) that in Black bluff occur "stratified 



horizontal lines of light-graj calcareous conglomerate or cement, in which are embedded Bundrj 

 fossils characteristic of and belonging i" tic Tertiai'j age, such as Cardium gra nlandicum, < '. deeo 

 ruin,. <i.i i tarti pectunculata, etc." It is true thai tin- general appearance of tin' el iff would 

 indicate tuch i state of affairs, bul when the structural details are closely studied ii is found thai 



while ili'' i-lin lii- (i so whal stratified appearance that might have been due to n puddling of the 



cinders and ashes of which it is composed, tli" fossils ar mfined i" a clay rock whicl curs in 



much on mile I fragments IV a few inches to two feet In diameter. These are scattered with some 



irregularitj and not copiouslj through the mass, and are in all stages "t decomposition incideul 

 to the agencj of heat and moisture, rhe evidence would app conclusive that these fi 



ments were caught u] ichanicallj : I nl nd distributed through the 



i during its ere il ion, 



