228 On the & I logy of tJu Basin of the 



I have regarded them as transported not by glaciers, but by 

 icebergs. 



Possibly Bome pari of this Drift material may have accumu- 

 1 along the margin of the greal glacier, moved by its 

 agency : but in thai ease we should expect to find in it abun- 

 dant fragments of the rocks which ontcropinthe region under 

 consideration, whereas I have rarely, it' ever, seen in these Drift 

 gravels any representatives of the rock.- underlying the south 

 margin of the lake basin. 



By whatever agency transported, the Drift gravels have, like 

 the boulders, for the most part come from some remote point 

 at the North, and were once spread broadcast along the south- 

 ern Bhore of the inland iceberg-bearing sea. 



In the retreat of the shore line during the contraction of the 

 water surface down to its present area, every part of the Blope 

 of the southern Bhore between the present water surface and 

 the highest lake level of former times, i. < .. all within a verti- 

 cal height of 300 feel or more, must in turn have been submit- 

 ted to the action of the Bhore waves, rain, and rivers, by which 



if, as is probable, the retrograde movement of the water line 



was Blow, these loose materia!-, would be rolled, ground, sort- 



ifted, and shifted, 60 that comparatively little would he Left 



in it- original bedding; the fine materials, clay and sand, 



would be washed OUl and carried further and still further into 



the lake basin, and spread over the bottom, to form, in Bhort, 

 the upper sandy layer- of the Drift. 



A - certain points in it^ deSCenl the water level seem- to hav( 

 been for a time stationary, and BUch points are marked by ter- 

 races and the long lino of ancient beaches which have been 



•red to. .\ similar "lake ridge" now borders the south 

 shore of hake Michigan, where it may be observed in the pro- 



of formation ; and thi to ho the legitimate effeel of 



wav< - everywhere on a Bloping shore composed of loose mate- 

 rial; storms driving tip sand and gravel to form a ridge which 

 Ultimately a barrier to the waves that built it. Wil 



