Fairbanks.] 



Geology of Point Sal. 



9 



mesa terrace rest directly on these benches, showing them to be 

 older. Although the upper part of this mesa appears to be a 

 detrital slope, the lower has more the appearance of a submarine 

 deposit. 



MIOCENE. 



Bituminous Shales. — The bituminous shales form the upper hori- 

 zon of the Miocene within the area mapped, being quite sharply 

 defined from the gypsiferous clays below. There is a small expo- 

 sure of these rocks on the little point about a mile and a half north 

 of Point Sal. Here they consist of flinty strata, dark shales, and 

 limestone richly impregnated with bituminous matter. They have 

 suffered much disturbance, and are contorted in a marked degree. 

 At one spot a syncline perhaps 25 feet across has been cut away in 

 such a manner as to leave a natural arch, the faces of which corre- 

 spond to the stratification. 



In the southern portion of the map there is an arm of the bitu- 

 minous shales, occupying a position between the serpentine and the 

 ocean. They are well exposed at the mouth of the canon below 

 the dairy, where they rest on or against the serpentine. They have 

 undergone compression and are greatly contorted. The basal por- 

 tion of the series is composed chiefly of clear, flinty rocks, showing 

 abundant remains of organisms visible to the unaided eye. The 

 flints are very regularly banded, those of clear opaline appearance 

 alternating with bands of a duller color and less silicious composi- 

 tion, in an exposed thickness of about 100 feet. 



The contact with the serpentine is not visible in the cliffs on the 

 coast. It is probable that extensive faulting has taken place along 

 the peridotite-gabbro axis, for the nearest exposures of the shale 

 have a vertical dip, while the adjoining serpentine is greatly crushed. 

 The dip of the shales gradually becomes less to the south away 

 from the serpentine. They can be traced for about 2,000 feet, and 

 then disappear beneath the Pleistocene sands. Nowhere in the 

 rocks of this series has the author observed any more regularly 

 fissile and banded structures. The total thickness represented here 

 can not be less than 1,000 feet. No fossils were found except Pecten 

 peckhami, Gabb, which seems to be confined to rocks of this char- 



