330 PAIGE AND KNOPF STEATIGRAPHIC SUCCESSION IN ALASKA 



lated with the Naknek (Upper Jurassic of Cook inlet), at the base of 

 which a very similar accumulation occurs. 



Lower Cretaceous 



Eocks of Lower Cretaceous age are represented mainl}' by but a single 

 formation — -a massively bedded limestone, 300 feet thick, which overlies 

 the Upper Jurassic rocks conformably. The limestone is very finely 

 saccharoidal in texture and white in color. A characteristic feature is its 

 strong, fetjd odor on fresh fracture. The age determination of this lime- 

 stone is based on the presence of Aucella a-assicolHs Keyserling, obtained 

 by Mendenhall. It may thus be seen that the rocks from the upper part 

 of the Middle Jurassic through the Lower Cretaceous are in conformable 

 succession. 



Tertiary 



The next youngest rocks of the region are of Upper Eocene (Kenai) 

 age. They are a series of shales, sandstones, and conglomerates contain- 

 ing workable seams of high-grade bituminous coal of a maximum thick- 

 ness of 17 feet.* A section exposed in Castle mountain shows 1,000 -|- feet 

 of conglomerate at the base, overlain by sandstones and shales. At least 

 3,000 feet of these sediments were observed in a locality on Chickaloon 

 creek. 



The nature of the relations of these rocks to the Mesozoic series is yet 

 in doul)t. There are reasons, however, for believing that they overlie 

 them unconformably. 



No marine fossils have been found in this series, but floral remains, 

 rather poorly preserved, are at times quite abundant. Dr F. H. Knowl- 

 ton rejjorts the following forms : 



Sequoia langsdorfli (Brgt.) Heer. Tu.rodluiii. dhtichinii jiiioccnum Heer. 



Ficus ? gronlandica Heer. Taxodimn tiiiajonnn Heer. 



Magnolia inglvfeldi Heer. Pali urns colouihi Heer. 



Fopuluft artica (?) Heer. Fruits, cf. Lcgiiiiiiiiofdtcs op. 



Rhamnus eridaiii Heer. Age, Kenai (Upper Eocene). 



Vihiirnum sp., cf. V. nordcnxl-iohJi Heer. 



Overlying the older rocks is a series of nearly horizontal lava flows, 

 basaltic in character. With their tuffs and breccias they attain a thick- 

 ness of 1,000 feet. They are definitely known to overlie fluviatile con- 

 glomerates of post-Lower Cretaceous age, and probably rest on the Kenai 

 so that their age is ]\Iiddle Tertiary or younger. 



* G. C. Martin : A i-econnai«sance of the Matanuska coal field, Alaska. Bull. no. 28l>. 

 U. S. Geol. Survey. 



