470 



SCIENCE. 



[N. S. Vol. VIII. No. 197. 



sition of specimens of this marble from a 

 deep test pit at one of the quarries is very 

 remarkable, no less than eighteen elements 

 having been detected in its analj'sis. 



9. Fluctuations of North American Glaeia- 

 tion shown by Interglacial Soils and Fossilifer- 

 ous Deposits. By Waeren Upham, St. Paul, 

 Minn. From a comparison of our conti- 

 nental drift deposits with the present re- 

 treatal conditions of the piedmont Mala- 

 spina glacier in Alaska, it is concluded that 

 the fauna and flora adjacent to the retiring 

 ice-sheet were nearly like those of the same 

 latitudes to-day, and that fluctuations of 

 the ice border to the extent of a few miles, 

 a few score, or a few hundred miles, more 

 acceptably account for our interglacial beds, 

 former surface soils and leached subsoils, 

 than a general departure and renewal of the 

 ice-sheet. 



10. Time of Erosion of the Upper Mississippi, 

 ifinnesota and St. Croix Valleys. By Waeeen 

 TJpHAM. Until the Ozarkian epoch of great 

 elevation of the northern part of this conti- 

 nent, inaugurating the Quaternary era, the 

 upper part of the present Mississippi basin, 

 above the vicinity of Dubuque, appears to 

 have been drained northerly, according to 

 recent studies by Hershey (Ame7-ican Geolo- 

 gist, Vol. XX., pp. 246-268, October, 1897). 

 After the Cretaceous marine submergence 

 of the State of Minnesota, its chief river 

 system probably flowed through the Eed 

 River Valley to Hudson Bay during the 

 Tertiary era, being reversed to take nearly 

 the course of the Minnesota and Mississippi 

 Rivers at the end of that era. The St. 

 Croix Eiver is thought by the author to 

 have obtained its passage through the rock 

 gorge of the Dalles at Taylor's Falls, Minn., 

 so late as the Buchanan Interglacial epoch, 

 preceding the Illinoian and lowan glacial 

 readvance ; and the channel of the Missis- 

 sippi from Minneapolis to Fort Snelling, 

 eroded during the Postglacial period, has 

 afforded to Professor N. H. Winchell his 



well-known estimate of that period a» 

 between 7,000 and 10,000 years. 



11. Supposed^ Corduroy Road'' of Late Gla- 

 cial Age, at Amboy, Ohio. By Professor G. 

 Frederick Wright, Oberlin, Ohio. This 

 paper detailed the discovery of a series of 

 logs lying side by side as in a corduroy 

 road, and extending for a distance of 20O 

 feet or more, which were covered by 30 feet 

 of gravel, in which were found the tooth 

 and tusk of a mammoth, the tusk being 10 

 feet long, 22 inches in circumference at the 

 base, and weighing 155 pounds. The resem- 

 blance to a corduroy road was, indeed, very 

 striking, but the appearance of the logs 

 showed that they were driftwood, and had 

 been buried by the accumulation of the 

 gravel that took place along the old shore 

 of Lake Erie, when, during the closing cen- 

 turies of the Glacial period, the water was 

 held up to a level 1 50 feet higher than now. 

 The logs and base of the deposit are 140 feet 

 above the lake and about 4 miles back from 

 it, on the banks of Conneaut Creek, in the 

 extreme northeastern corner of Ohio. The 

 gravel was evidently brought down from 

 the higher lands of the south, near the 

 sources of the creek, and was deposited 

 with the mammoth remains in a delta at 

 the edge of this old glacial lake. In con- 

 nection with this investigation it was ascer- 

 tained that similar deltas of gravel charac- 

 terize the margin of the old lake where 

 other streams from the south met it at vari- 

 ous places between this point and Cleve- 

 land. Altogether, these observations give 

 a very vivid picture of the rapidity with 

 which coniferous forests proceeded to cover 

 northern Ohio as the ice melted back, and 

 of the promptness with which the immense 

 animals of the time reoccupied the terri- 

 tory. Important inferences are also de- 

 rived, showing that the period of time dur- 

 ing which the water remained at the high 

 levels of the old ice-dammed lakes was 

 short. 



