192 RECORD OF SCIENCE FOR 1886. 



Grand Traverse Bay, at the moutli of the Illiuois River, and along tlie 

 lower part of the Wabash; but this may be due to fuller records from 

 these places. In general, it is found that the size of the masses de- 

 creases as their distance from the Lake Superior region increases, and 

 it is thought that, with some possible local exceptions, the latter has 

 been its source.* 



7. In a paper on the geology in the vicinity of the ISTorthern Pacific 

 Eailroad, Newberry t gives an account of his observations on the drift. 

 In the Yellowstone Valley he was unable to find the evidences of the 

 eastern drift reported by C. A. White, and considers the drift of the 

 upper Missouri local in character. 



8. Oomstock describes some features of the drift in the Rocky Mount- 

 ains of Wyoming and Colorado. All the glacial action is iuferred to 

 have been local, but intense. In the San Juan district, and to a less 

 extent elsewhere, a "distinct peculiarity lies in the duplex character of 

 the erosion ; that is to say, there are two zones of glaciation vertically, 

 the upper largely representing the transportative action, the lower 

 being eroded without removal of the debris to any extent. The imper- 

 fect drainage had fastened the ice sheet so that it could move as a unit 

 only in the superficial portion, while the lower part acted like a slowly 

 working plow, which cut deeply but not so extensively as the overlying 

 mass. In the more elevated tracts, therefore, the lower portion often 

 lies in grooves like culs-de-sac, and many of these exist to-day, connected 

 with the main drainage often by reversed or indirect drainage." | 



9. In his paper on the Post-tertiary elevation of the Sierra Nevada, 

 Le Conte incidentally discusses the later history of the Mississippi 

 Basin. He concludes that during the Champlain period it was filled 

 with 400 feet or more of deposits ; that in the terrace period elevation 

 took place, and the present wide channel was cut, — not by cliff erosion 

 as in the Grand Cation, but by shifting of the stream from side to side, 

 and that in the present epoch there has been subsidence and, as shown 

 by Hilgard, a refilling with about fifty feet of alluvium. § 



10. In a paper on the Geology of Long Island, F. J. H. Merri 11 makes the 

 interesting statement that the morainal hills owe their elevation in great 

 part to a series of folds at right angles to the course of the glacier, and 

 involving the pre-glacial deposits. The deep bays in the north shore 

 of the island appear to have been plowed across these flexed beds, and 

 are found to be heavily flanked by ridges and hills. From the thinness 

 of the till deposits south of Long Island Sound (except opposite its 

 western extremity) it is thought that the depression was pre-glacial, 

 and the ice sheet lost the loads of detritus in its lower portion and 

 attached to its base in passing over the broader part of the Sound, 

 only carrying across the bowlders and d6bris upon its surface. The 



* Wiscousin Acad. .Sci., etc., Trans., vol. 6, pp. 42-50. 

 tNow York Acad. Sci., Auuals, vol. 3, pp. 242-270. 

 t American Naturalist, vol. 20, Nov., 1886, pp. 925-927. 

 § Am. Jour. Sci. Iil, vol. 32, pp. 167-181. 



