986 



SCIENCE. 



[N. S. Vol. XV]. No. 416. 



liable data were obtained in regard to tlie 

 northern and western front of the Alaskan 

 Eange, which had . not previously been ex- 

 plored. The position and altitude (the latter 

 with a probable error of not over 100 feet) 

 was determined by Mr. D. L. Eeaburn, topog- 

 rapher of the expedition. It is of interest 

 to note that Mt. McKinley is definitely de- 

 termined to be over 20,000 feet and Mt. For- 

 aker 17,000 feet. 



The notes and specimens having not yet 

 been studied, but few statements can be made 

 in regard to the bed-rock geology, which is 

 complex and embraces terranes from the Si- 

 lurian to the Carboniferous. 



The oldest terranes were found in the 

 northern part of the area, and consist of a 

 metamorphosed conglomerate, ■ often having a 

 gneissic phase. The lowest member of this 

 series is not distinguishable from a true 

 Archaean gneiss and it possibly belongs to a 

 crystalline basal complex. Overlying the con- 

 glomerate, a slate and phyllite series was 

 found, succeeded by limestones and slates 

 and arenaceous beds carrying Ordovician fos- 

 sils. Devonian limestones were found widely 

 distributed. The Paleozoic rocks are in- 

 tensely folded and faulted. At least one, and 

 probably two, unconformities occur within the 

 Paleozoic, one near the base of the Devonian 

 and a second probably in the Silurian. 



In the southern part of the area there is 

 a vast thickness of shales, slates, grits and 

 sandstones, in which Jurassic fossils were 

 found. These were, in the section studied, 

 well exposed across the range. This series 

 thins out to the northward, and near the 

 Tanana is entirely wanting. It is 'overlaid 

 unconformably by sandstones, conglomerates 

 and shales, which earrj^ coals. The plant re- 

 mains from these beds, studied by Dr. F. II. 

 Knowlton, show it to be of Arctic Miocene 

 or Eocene age. These Tertiary beds have a 

 limited development in the southern part of 

 the belt, but thicken to the northward. On 

 the Cantwell a section of 3,000 feet was mea- 

 sured. The only other consolidated beds 

 found in the region were some lignitic bear- 

 ing friable sandstones, which were found in 

 the southern part of the belt. These aggre- 



gate probably not over 200 feet and are prob- 

 ably of late Tertiary age. 



Among the plentiful intrusive rocks there 

 are two important lines of granite, one east 

 of the nrountains along the axis of the Sush- 

 itna Valley, and a second along the axis of 

 the Alaskan Range, where the highest peaks, 

 such as Mt. McKinley and Mt. Foraker, are 

 probably chiefly made up of granite. Various 

 other granular rocks occur as dikes and stocks. 



Extrusive rocks are found along both flanks 

 of the range, but do not seem to compose the 

 range itself. They are mainly of post-Eocene 

 age. The active volcanoes of the Aleutian 

 Islands and the Alaskan Peninsula do not ex- 

 tend into the region under discussion, though 

 some of their ejecta are found mingled with 

 the recent alluvial deposits. 



Evidence of glaciation is abundant in the 

 region south of the Tanana Valley. Glacial 

 till and erratics were found along the western 

 shore of Cook Inlet, and are closely associated 

 with stratified sands and gravels. The foot- 

 hills of the main range, 2,000 feet high, forty 

 miles inland, were found glaciated, and, going 

 westward into the mountains, the upper limit 

 of glaciation was found at an altitude of about 

 4,000 feet. On the north side the base of the 

 mountains is glaciated and the valleys up to 

 4,000 or 5,000 feet wide. On both sides of 

 the range there are heavy gravel deposits, 

 which mantle the base of the mountains. 

 These are interpreted as overwash deposited 

 during the retreat of the ice. Remnants of 

 this greater ice sheet are to be found in the 

 glaciers which now occupy many of the higher 

 valleys, on both slopes of the Alaskan Range. 

 Alfred H. Brooks, 



Secretary. 



BIOLOGICAL SOCIETY OF WASHINGTON. 



The- 361st meeting was held on Saturday, 

 November 29. 



William Palmer discussed the ' Variation 

 of the Downy Woodpecker in Eastern Mary- 

 land and Virginia.' The speaker showed the 

 extent of variation of the white markings of 

 the wing coverts of the two subspecies found 

 in the above region, as well as that of inter- 

 grading individuals. Dryohates puhescens 



