622 



SCIENCE. 



[N. S. Vol. IX. No 226. 



that there was almost an exact accordance be- 

 tween the diurnal range in magnetic diclination, 

 horizontal and vertical form. When the fluc- 

 tuations in these elements from day to day were 

 compared, however, there were remarkable 

 periods of coincidence, combined with non-co- 

 incidence. It was shown that the curves for 

 grains in a cubic foot of air and for pressure 

 fluctuations were exactly coincident at St. 

 Louis, Mo. When these curves were compared 

 with the magnetic curves there was no difficulty 

 found in matching them with one or another of 

 the latter. This seemed to show an intimate 

 connection between the phenomena, and it now 

 remains for those versed in terrestrial magnet- 

 ism to explain the want of coincidence in the 

 phenomena. E. D. Preston, 



Secretary. 



GEOLOGICAL SOCIETY OF WASHINGTON. 



At the regular meeting of this Society, held 

 in Washington, D. C, on April 12, 1899, Mr. 

 Alfred H. Brooks communicated some ' Notes 

 on the Geology of the Tanana and White River 

 Basins, Alaska.' 



The region embraces the Lower White and 

 the major part of the Tanana River, both trib- 

 utary to the Yukon. To the south the area is 

 bounded by a part of the St. Elias range, by 

 the Natzutin Mountains and by the Alaskan 

 range, and lies chiefly in the region of the dis- 

 sected Yukon plateau. 



A complex of gneisses, gneissoid and massive 

 granites, with some dioritic rocks, are believed 

 to be the basal series. They are succeeded by 

 metamorphic rocks which have been differen- 

 tiated into three groups. These are unconform- 

 ably overlaid by the Wellesley formation, con- 

 sisting chiefly of conglomerate, of Devonian or 

 Carboniferous age. On the Lower Tanana 

 some sandstone and slate beds were noted and 

 called the Nilkoka beds, and these are probably 

 also Paleozoic. These have all sufiered con- 

 siderable deformation and often carry mineral- 

 ized quartz veins. In the older and more 

 altered rocks the quartz is more plentiful thau 

 in the younger beds. Assays of a number of 

 samples gave traces of both gold and silver. A 

 small area of very slightly deformed soft yellow 

 sandstone was tentatively classed as Eocene. 



The position of two systems of structure lines 

 goes to show that the deformation of the region 

 was caused by two synchronous thrusts coming 

 from different directions, and these were prob- 

 ably lines of movement during several periods 

 of deformation. 



The summits of the old plateau remnants are a 

 striking feature of the region and mark an old 

 peneplain. During the late Tertiary time this 

 peneplain was elevated and probably somewhat 

 deformed and was then deeply dissected. The 

 evidence goes to show that the drainage of the 

 upper Tanana and middle White then flowed 

 southeast and probably found its way to Lynn 

 Canal by way of the valleys of the Nissiling, 

 upper Alsek and Chilkat Rivers. A depression 

 succeeded the uplift, and the partially drowned 

 valleys were then filled with sediments. To- 

 ward the close of this period of depression the 

 White River Valley was occupied by ice, and 

 probably a little later glaciers moved down 

 some of the southern tributaries of the Tanana. 

 No evidence of general glaciation was found in 

 the region. The last orographic disturbance 

 was the elevation of the land mass to about its 

 present position, and this caused a partial dissec- 

 tion and terracing of the sediment of the older 

 valleys. 



Mr. J. S. Diller exhibited specimens of Paleo- 

 trochis which had been described in 1856 by E. 

 Emmons as siliceous corals and regarded as the 

 oldest fosssils known. Professor James Hall 

 regarded them as concretions. Professor J. A. 

 Holmes, of North Carolina, examined the rock 

 in the field and considered it of igneous origin, 

 while Mr. C. H. White, who examined the 

 specimens collected by Holmes, pronounced the 

 forms organic. Nitze and Ilauna, of the Geo- 

 logical Survey of North Carolina, maintain the 

 igneous characters of the rock, and this view is 

 strongly supported by Mr. Diller, who showed 

 that the supposed fossils and concretions are 

 spherulites in a more or less altered rhyolite. 

 Mr. Diller's paper will be published in full in 

 the American Journal of Science. 



W. F. MORSELL. 



U. S. Geological Survey. 



CHEMICAL SOCIETY OF WASHINGTON. 



The regular meeting was held on March 9, 

 1899. 



