396 STANTON AND MARTIN — MESOZOIC SECTION ON COOK INLET 



of Gabb's California species shows that they are not separable. The 

 species belongs to the group of Pseudomonotis ochotica, which is character- 

 istic of the Upper Triassic of Siberia and the boreal regions generally. 



In California Pseudomonotis sub circular is is confined to the Swearinger 

 slates, which form the uppermost Triassic formation of that region. Sim- 

 ilar beds with the same fossil occur in Vancouver and Queen Charlotte 

 islands and on the mainland of British Columbia, and they cover con- 

 siderable areas in the Copper River region of Alaska. 



At Bear bay the much folded Triassic limestone yielded imperfect 

 specimens of a Halobia, and at Cold bay a few imperfect Ammonites 

 not generically determined were obtained in beds overlying the Pseudo- 

 monotis layers, but possibly still within the Triassic. 



One other area of probable Triassic has been reported by Hyatt* from 

 cape Thompson, northwest Alaska, on account of the supposed occur- 

 rence of Halobia or Daonella there, but subsequent collections from that 

 region have proved the rocks to be Paleozoic. 



LOWER JURASSIC 



In the neighborhood of Seldovia there is a considerable thickness of 

 sedimentary and associated igneous rocks that are believed to be Lower 

 Jurassic. They lie west of the cherts previously mentioned as of prob- 

 able Triassic age, and are not so much disturbed and metamorphosed as 

 the cherts, from which they are doubtless separated by an unconformity, 

 though the dips, which vary in both direction and amount, average per- 

 haps 40 or 50 degrees and in some exposures are as much as 70 degrees. 

 The rocks are apparently composed almost exclusively of fragmental 

 igneous material, and should be classified as tuffs rather than sandstones 

 and conglomerates. The fine grained beds are dark greenish gray when 

 fresh, but weather to lighter shades, while some of the coarser beds, made 

 up of more or less angular fragments, are red, greenish, and variegated. 



This series was seen on the west shore of Seldovia bay at the entrance 

 to the harbor and for 3 miles westward along the shore of Cook inlet ; 

 also on the east shore of port Graham south of the coal-bearing Kenai 

 exposures. At the latter locality the section includes a conspicuous bed 

 of light colored cherty limestone (see plate 67, figure 2). It is probable 

 that the ''dense Neocomian limestone" near English bay, from which 

 Eichwald cited Arcomya crassissima and a Janira, belongs in this series. 



Fossils are not very abundant nor well preserved, but those obtained 

 on Seldovia bay and along the coast for 2 miles to the westward indicate 

 a horizon low in the Jurassic. They include Pentacrinus, a Trigonia of 

 the section Glabra?, Cardinia (?), Myophoria (?), Gryphsea, three or more 



♦Seventeenth Ann. Rept. U. S. Geol. Survey, p. 907. 



