Geology and Mineralogy. 305 



on the central and greater part of its area are thought to have 

 carried much drift upward from the ground into the lower fourth 

 or third part of the ice, the rate of its ascent being perhaps one 

 or two degrees, which would give a rise of 90 or 180 feet in a 

 mile. During the final melting and retreat of the ice-sheet, its 

 large volume of englacial drift was deposited, partly as ground 

 moraine or subglacial till carried down by descending currents in 

 the outer part of the ice within distances estimated to range from 

 10 or 20 to 50 or 100 miles back from the ice boundary. Another 

 large part of the englacial drift became exposed on the ice sur- 

 face by its ablation and fell loosely as the ice melted away, form- 

 ing the upper part of the till; but much of this superglacial drift 

 was washed away by the glacial streams and deposited as the 

 stratified gravel, sand, and clay, called modified drift. 



In a second paper on the Succession of Pleistocene formations 

 in the Mississippi and Nelson River Basins, the Lafayette forma- 

 tion and the Saskatchewan gravels were referred to fluvial depo- 

 sition during an epeirogenic uplift initiating the Pleistocene 

 period and culminating in the accumulation of the continental 

 ice-sheet. The till and marginal moraines record the maximum 

 extent and stages in the recession of the ice. Loess and other 

 stratified drift deposits were mostly laid down during the glacial 

 recession, being supplied from englacial drift, as likewise were the 

 deltas of Lake Agassiz for their larger part. Depression of the land 

 during the Glacial period and its reelevation while the ice-sheet 

 was retreating are well shown by the loess, the beaches of Lake 

 Agassiz, and marine beds about Hudson Bay. (Author's abstract.) 



N. H. Darton in his paper on Cenozoic History of Eastern 

 Maryland and Virginia " gave a brief account of the topography 

 and structure of the region, and of the salient feature of the 

 Cenozoic members, and a summary of the history of a series of 

 deposition intervals and tiltings in the general Cenozoic emerg- 

 ence. The principal feature of the paper was the announce- 

 ment of the discovery of an erosion interval between the upper 

 and lower Columbia terraces eastward due to tilting from the 

 northwestward during the Columbia uplift. Off to the east and 

 south the later Columbia lies on earlier Columbia, in places beau- 

 tifully differentiated, in the normal sequence." (Author's abstract.) 



H. F. Reid in his public lecture on " Glacier Bay, Alaska," 

 said that Glacier Bay is the most accessible region in which to 

 see large tidewater glaciers. There are eight glaciers which dis- 

 charge bergs into its waters. The largest of these is Muir Gla- 

 cier which drains an area of about 800 square miles. It is mov- 

 ing with a maximum velocity of about seven feet a day, and is 

 continually discharging large icebergs from its end. It has 

 extensive gravel deposits which present many interesting features. 

 Its fluctuations have been great within recent times. One or two 

 hundred years ago it extended, in common with the other glaciers 

 of the bay, twenty miles below its present ending; and not long 

 before that, the glaciers were so small, that valleys now barren 



Am. Jour. Sol— Third Series, Yol. XLYI, No. 274. — October, 1893. 

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