THE JURASSIC FLORA OF (WPE LISBURNE, ALASKA. 



Bv F. IL Knowlton. 



INTRODUCTION. 



A })eculiar and iibsorbiiig interest attaches to the study of the fossil floras of the arctic 

 regions, for they indicate climatic conditions very unlike those now existing m those regions. 

 In place of the present snow and ice and the scant, almost perpetually frozen soil which sup- 

 ports but a handful of depauperate plants, the conditions from at least late Paleozoic to 

 middle Cenozoic time made an abundant and luxuriant vegetation possible, at least during 

 certam periods. ^Vlthough these lands are now so mhospitable, and hence but rarely visited, 

 an astonishiiig amount of information concernmg their fossil floras has been accumulated, 

 and to this kiiowledge Alaska has contributed its full quota, though doubtless much more 

 will ultunately be lvno^\^l. 



The recent i)ublication of a report by Prof. A. C. Seward on the Jurassic plants of Amur- 

 land, long kno\vn from the historic researches of Oswald Heer, has called to mind the existence 

 of a considerable collection of similar plants from the vicinity of Cape I^isburne, Alaska, 

 that has been m my possession for a number of years. As it is now possible, with Seward's 

 paper in hand, to recognize still further the strildng resemblances between the Jurassic floras of 

 Alaska and Siberia, it seems an opportune time to present the results of this recent study. A 

 prelimmarj' examination of this material was made, and certain tentative identifications were 

 adopted in a short report for the use of the geologists who collected it, but this is the first 

 time it has been aderiuatelj^ described and figured. 



The material considered in this paper was collected in 1904 by Arthur J. Collier, of the 

 United States Geological Survey, while engaged in a study of the geology and coal resources 

 of the Cape Lisburne region.' The coal dejiosits are extensive and are the only mineral re- 

 sources of the region kiiowm to be of commercial importance. Collier describes the locality as 

 follows: 



Cape Lisburne is the bold headlaiul which marks the northwestern extremity of a land mass projecting into 

 the Arctic Ocean from the western coast of Alaska between latitudes 68° and 69°. It lies 160 miles north of the 

 Arctic Circle, about 300 miles directly north of Nome, and is the only point in Alaska north of Bering Strait where 

 hills above 1,000 feet in height approach the sea. 



So far as known, the rocks of the Cape Lisburne region are all sedimentary. The age 

 represented, with the approximate thickness of each, is given by Collier as follows: Devonian ( ?), 

 2,00n+ feet; Lower Carboniferous [Mississippian], 4,500+ feet: I^pjier Jurassic, 15,000+ feet; 

 Lower CretaceousXO) 10,000+ feet; Pleistocene. 50 feet. 



THE C ORWIN FORMATION. 



The Jurassic section to whicli tlic name Corwiii fonnatiou lias been given is described by 

 Collier^ as follows: 



The older of the Mesozoic formations, which takes its name from Corwiii Bluff and tlie coal mines there located, 

 is best exposed on the coa.st at a point 26 miles cast of Cape I.isljurne and thence extends norlheastward (« Cap(^ Beau- 

 fort, a di.itance of 40 mile.s. which i.s the limit of this investigation. It is known to occur again near Wainwright lidet 



' U. S. Gcol. Survey Bull. 278, pp. 1-54, Pis. I-IX, 1906. ' Op. cit., p. 27. 



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