GLACIAL FLOW AS ] AC TOR IN DRUMLTN FORMATION 733 



a perfectly horizontal valley side edjce, and some of them are more than 50 

 miles long. I have no doubt but that at the same time lake and stream de- 

 posits were accumulating in different places, and also in the same place at 

 different times, but the great extent of the horizontal upper surface, the fine- 

 ness of the material and regularity of stratification, the fossils, and the shore 

 features where developed seem to me to show conclusively that most of the 

 filling on many of the streams tributary to the Mississippi and Ohio was laid 

 down in quiet ponded water. 



.RADIATION OF QLACIAL FLOW AS A FACTOR IN DRUMLIN FORMATION 

 BY WILLIAM C. ALDEN 



(Abstract) 



This discussion is based on the relations of the moraines and drumlins of 

 the south half of the Green Bay glacier of eastern Wisconsin. There is a very 

 notable development of drumlins which are grouped in three more or less dis- 

 tinct sets. Corresponding to each is a set of marginal moraines believed to 

 mark the limits of the glacial lobe during the stages when the drumlins were 

 being formed. The outer moraine of each set marks the limit of a readvance 

 of the ice following an interval of recession. The drumlin belts in each case 

 are confined to distances of 30 to 35 miles from the south end of the lobe — 

 that is, to that part where the ice was radiating widely to the curved margin 

 of the lobe and where it was thinned in consequence of the radial spreading 

 and of loss by melting and ablation. 



The computations of the probable elevation of the surface of the glacier 

 were based on the known thickness of the ice within four miles of the margin 

 where the Baraboo quartzite range was over-ridden and on an estimated aver- 

 age slope for this surface of 50 feet per mile in the first 25 miles, including 

 the initial rise of TOO feet in the first four miles and allowing an average of 20 

 feet per mile thereafter. Deducting from these the present elevation of the 

 land gives a thickness of ice varying from 1,450 feet over the initial part of 

 the first drumlin belt to 450 to 830 feet, where drumlins ceased to be formed 

 within five miles of the limit of ice advance. The drumlin-forming ice stream 

 had an initial width at A of 17 miles where radiation began. In advancing 15 

 miles this expanded to a width of 32 miles at B, and at the terminal moraine 

 the expansion gave a marginal arc of about 100 miles. Computations show 

 that in spreading to the width at B, while at the same time maintaining the 

 requisite thickness and low surfical slope, the cross-section of the stream 

 must have increased to 1.603 times the area of the initial section, and. inas- 

 much as no tributary stream had added to the volume, the rate of flow must 

 have been faster at A than at B. At C, where the drumlin formation ceased, 

 the arc of the stream had expanded to 85 miles and the cross-section was 

 2.325 times that at A and 1.45 times that where drumlin formation began. 

 From these figures it is evident that the spreading of the ice under its own 

 weight alone would not account for the remarkable expansion. Only the for- 

 ward crowding of the more rapidly moving ice in the rear could have supplied 

 the requisite volume. Though the stream expanded greatly so that friction 

 was much increased, the remarkable development of drumlins indicates that 



