182 



SCIENCE 



[N. S. Vol,. XXV. No. 631 



to the soutli the same series is much meta- 

 raorphosed, sometimes to complete recrystal- 

 lization, and intrusives are abundant. The 

 next member is made up of limestone which 

 on the Porcupine is about 600 feet thick and 

 carries Ordovician fossils. This terrane com- 

 prises bluish-gray, non-magnesian limestones, 

 distinguishable lithologically from the buff 

 dolomitic series which follows them, but has 

 not been definitely recognized in other parts 

 of the province. The relation of these Ordo- 

 vician beds to the older rocks is probably one 

 of unconformity. 



The Silurian is represented by at least 2,500 

 feet of magnesian limestone with some quartz- 

 ites and slates, which are probably conform- 

 able to the Ordovician. Its correlation with 

 the Fortymile series of Spurr is suggested but 

 not proven. When the Devonian is con- 

 sidered, the problem becomes more complex, as 

 no complete section of these rocks has yet 

 been found. In general terms it can be said 

 to be made up of shales, slates and cherts, with 

 some limestones, while locally ancient lava 

 flows and tuffs dominate over the sediments. 

 On the Yulion the igneous rocks are very 

 much more abundant than the sediments, 

 while on the Porcupine the sediments are 

 most abundant. The thickness is much in 

 doubt, but can not be less than 3,000 feet and 

 may be twice as great. The relation of the 

 Devonian to the Silurian is unknown, but is 

 probably one of unconformity. A black shale 

 and slate bed some 1,300 feet thick constitutes 

 the upper member of the Devonian and within 

 this formation is prohably the dividing line 

 between the Devonian and the Carboniferous. 



In this province the Oarhoniferous em- 

 braces about 4,000 feet of sediment, usually 

 characterized by an absence of igneous rock. 

 Overlying the shale mentioned above is about 

 1,000 feet of a thin-bedded limestone and 

 shale series which carries Carboniferous fossils 

 which have not yet been studied in detail. 

 After these limestones and shales were laid 

 down, the character of the sediments changes 

 abruptly, indicating possibly a period of ero- 

 sion. A heavy bed of chert conglomerate 

 forms the basal member of the higher series 

 and this is succeeded by shales, sandstones 



and conglomerates with an aggregate thick- 

 ness of 1,600 feet. A limestone bed some 200 

 feet thick constitutes the youngest member of 

 the Carboniferous. This is overlaid in dif- 

 ferent parts of the province by younger ter- 

 ranes of various ages. On the Porcupine the 

 lowest member of the Devonian is a limestone 

 300 feet thick, while olive and chocolate- 

 colored shales, in part fossiliferous, appear to 

 comprise a large share of the Middle Devonian 

 sediments. 



The Stratigraphic Succession in the Region 



Northeast of Cook Inlet, AlasTca: Sidney 



Paige and Adolf Knopf. 



In this communication the combined re- 

 sults of the field studies of this region in 

 1906 were presented by Mr. Paige. The rocks 

 exposed in this geologic section were found to 

 range in character from garnetiferous mica 

 schists of probable pre-Silurian age to uncon- 

 solidated Pleistocene stream and glacial 

 gravels. Jurassic strata are very extensively 

 developed and are divided into two uncon- 

 formable formations, the lower of which con- 

 sists chiefly of andesitic breccias and amygda- 

 loids, 1,000 feet in thickness and overlain by 

 graywackes, shales, sandstones and con- 

 glomerates. Marine shells, found both in the 

 tuffs and in the graywackes, fix its age as 

 Lower Middle Jurassic. The younger Jurassic 

 rocks consist of shales, arkose, sandstones, 

 conglomerates with some interstratified tuffs. 

 The age indicated by fossil evidence ranges 

 from the upper part of the Middle Jurassic 

 through the Upper Jurassic. Conformably 

 overlying these rocks is a Lower Cretaceous 

 limestone 300 feet thick. 



The Upper Eocene (Kenai) rocks of this 

 section are freshwater sediments, consisting 

 of shales, sandstones and conglomerates folded 

 and carrying workable coal beds, of a maxi- 

 mum thickness of 17 feet. Their total thick- 

 ness is not less than 3,000 feet; their age was 

 determined on the fossil flora collected. 

 Basaltic lavas and tuffs overlie the older 

 rocks. They attain a thickness of 1,000 feet 

 and form the summit topography of the 

 region. 



