ABSTRACTS 



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GEOLOGY. — A geologic reconnaissance of the Iliamna region, Alaska. G. 

 C. Martin and F. J. Katz. Bulletin U. S. Geological Survey No. 

 495, pp. 138, with maps, sections, and views. 1912. 



The Iliamna region, as here denned, covers an area of about 5000 

 square miles, situated in southwestern Alaska, west of the southern half 

 of Cook Inlet and north of the Alaska Peninsula. Most of this field is 

 new to the geologist, and the work accomplished contributes facts, par- 

 ticularly with reference to the Mesozoic sequence, which may help eluci- 

 date the stratigraphy and structure of adjacent districts. 



The general stratigraphic section includes Quaternary deposits; Ter- 

 tiary basaltic flows and tuffs, with some sedimentary beds; upper and 

 Middle Jurassic shales, sandstones, and conglomerates; Lower Juras- 

 sic porphyries and tuffs; Upper Triassic limestone and chert; early 

 Triassic or late Paleozoic greenstone and slate; and Paleozoic gneiss, 

 schist, and crystalline limestone. 



The more important stratigraphic features of this region are the recog- 

 nition of the highly metamorphosed and presumably early Paleozoic 

 gneisses in a district where they had not been previously known; the 

 description of a newly discovered Triassic limestone containing an inter- 

 esting coral reef fauna of Noric age, which extends the known distribu- 

 tion of Triassic reef corals into a latitude (60° N.) far beyond their pre- 

 viously known range; the re-definition of the Jurassic formations of 

 Cook Inlet, which, because of the stratigraphic completeness of their 

 development and the abundance and variety of the fossils of their several 

 faunas and floras, constitute the best Jurassic section in North America; 

 and the recognition of a large area of Tertiary lavas. The provisional 

 lists of fossils consist however, chiefly of undescribed species. 



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