506 



SCIENCE, 



[N. S. Vol. XXV. No. 639 



its parent stock or preferential mating of like 

 forms for an explanation for the origin and 

 continuance of these closely related species in 

 a coincident environment. This is the solu- 

 tion which Darwin proposed to meet this dif- 

 ficulty. De Vries finds that the coincidently 

 appearing new elementary species of (Enothera 

 attain their full constancy at once. Isolation 

 plays no part in their origin or continuance. 

 Charles Atwood Kofoid 

 Univebsitt of Caufoenia 



note on a tertiary basin in northern 



Alaska' 

 Beds of Tertiary age are known in various 

 widely separated regions of Arctic and sub- 

 Aretic America. They occur generally in 

 basins of limited area in the older rocks. 

 Such basins are rather widely distributed in 

 Alaska. Brooks' has recently reviewed the 

 literature relating to those in Alaska. A 

 number of isolated Tertiary basins are known 

 in the islands of the Arctic Archipelago' and 

 others have been reported in the Northwest 

 Territory' east of northern Alaska. The age 

 of nearly all of the Tertiary beds which are 

 known in Arctic America has been deter- 

 mined from plant remains occurring in them, 

 80 that we have a very fair knowledge of 

 the plant life of northern America in Tertiary 

 times, but a very meager knowledge of the 

 invertebrate fresh-water fauna which lived 

 in some of the Tertiary lakes of Arctic 

 America. The discovery of such a fauna by 

 the writer during the past summer along the 

 Porcupine River in northeastern Alaska 

 seems, therefore, worthy of record. 



' Published by permission of the Director of the 

 U. S. Gfeological Survey. 



"The Geography and Geology of Alaska,' pro- 

 fessional paper U. S. Geological Survey, No. 45, 

 pp. 237-244, 1906. 



■ Low, A. P., ' Cruise of the Neptune,' 1906, pp. 

 226-229. 



•McConnell, R. 6., 'Report on an Exploration 

 in the Yukon and Mackenzie Basins, Northwest 

 Territory,' Can. Geol. Surv., Vol. 4, n. ser., Kept. 

 D, 1890. 



Camsell, C, Report on the Peel River and Trib- 

 utaries Yukon and Mackenzie, Can. Geol. Surv., 

 Vol. XVI., 1906, Pt. C, pp. 27-28. 



About one hundred miles above its junction 

 with the Yukon the Porcupine Eiver enters 

 the Yukon Flats, an alluvial plain without 

 topographic relief, through which the Yukon 

 Eiver flows for 200 miles. Before entering 

 the Yukon Plats the Porcupine traverses for 

 about 25 miles a belt of limestones of Paleozoic 

 age having a north and south trend and giv- 

 ing rise to low mountains and hills. Between 

 this belt of elevated country and a similar but 

 wider zone of topographic relief near the in- 

 ternational boundary extends a comparativdy 

 flat basin having a width of about 25 miles. 

 The north and south extent of this basin, 

 which Maddren has called the Coleen Basin,' 

 after the river draining its northern portion, 

 is unknown. There is good reason to believe, 

 however, that its north and south extent is 

 much greater than its width. The Porcupine 

 traverses this basin in wide sweeping mean- 

 ders. The migration of the channel of the 

 river along parts of its course through 

 this basin has left in places low banks 

 bordered by recent silts. An older set of sedi- 

 ments, however, constitutes the bulk of the 

 floor of the Coleen Basin. These older sedi- 

 ments are well exposed on the largest meander 

 in this portion of the river, known as the 

 Fish Hook bend, which shows continuous 

 bluffs for two or three miles, 40 to 100 feet 

 high, composed mainly of finely laminated 

 shale or clay. The dominant color of these 

 beds is light lemon yellow, which is varied 

 by patches of yellowish green, pink, and 

 brownish. At the upper end of Fish Hook 

 bend, on the west bank of the river, the fol- 

 lowing section was measured: 



Feet. 



1. Fine sand, soil and muck (top) 1-5 



2. Coarse gravel and sand 10 



3. Dark carbonaceous clay and old forest bed 0- 2 



4. Coarse gravel and sand 15 



5. Soft, finely laminated, drab-colored clay 



shale, with large ironstone concretions 

 in upper part, containing fresh-water 

 bivalves 70 



The fossils which were secured from the 

 ferruginous concretions occurring in divi- 



' ' Smithsonian Exploration in Alaska in 1904 

 in Search of Mammoth and other Fossil Remains,' 

 Smithsonian Misc. Coll., Vol. 49, 1905, p. 12. 



