54 



SCIENCE. 



[N. S. Vol. III. No. 54. 



■ing analysis of the accumulation and mo- 

 tion of glaciers. He distinguished the re- 

 gion of accumulation of snow in excess of 

 melting as the reservoir, and the region of 

 melting in excess of accumulation as the 

 dissipator ; the border line is the neve line. 

 By assuming cross- sections at various 

 points, the relative velocities of movement 

 were worked out on the basis of mechanics. 

 The same was done for a glacier which 

 spreads from a center in all directions. The 

 progress of the same layer of snow was then 

 traced from reservoir to dissipator and par- 

 allel lines of motion for the individual parts 

 were established, the neve line furnishing 

 a middle line. It was then shown that the 

 original stratification plane as indicated by 

 debris would at the end of the journej^ cut 

 these lines of motion and would emerge 

 with a high dip, a fact already observed on 

 some glaciers. The topic of the variation in 

 the advance and retreat of glaciers was dis- 

 cussed and the several explanations were 

 analyzed in detail. The paper was dis- 

 cussed by G. Frederick Wright and R. D. 

 Salisbury, the latter mentioning that the 

 thin fronts of Greenland glaciers showed 

 the upward tendency of stratification planes, 

 but that thick fronts lacked it. The Society 

 then adjourned until the following day. 



In the evening about sixty Fellows dined 

 together, with President Shaler and Pro- 

 fessor Emerson acting jointly as toastmas- 

 ters, and listened to some amusing speeches 

 by several members. 



On reassembling Saturday morning the 

 reading of papers was at once resumed. 



The Relation between Ice Lobes South from the 



Wisconsin Driftless Area. Frank Lever- 



ETT, Denmark, Iowa. 



Instead of a coalescence of ice lobes from 



the east and the west sides of the Driftless 



Area in the drift-covered district to the 



south there was an invasion and withdrawal 



of one lobe (the western) before the other 



reached its culmination. The eastern lobe 

 encroached upon territory previously glaci- 

 ated by the western, depositing a distinct 

 sheet of drift and forming at its western 

 limits a well-defined morainic ridge. There 

 appears to have been a period of considerable 

 length between the withdrawal of the west- 

 ern lobe and the culmination of the eastern. 



Subsequently, however, there was a read- 

 vance of the lobe on the west into uoi-th- 

 eastern Iowa, and this readvance appears 

 to have been contemporaneous with the 

 nearly complete occupancy of northwestern 

 Illinois by the eastern ice lobe. It seems 

 not improbable that the ice lobes were then 

 for a brief period coalesced for a short dis- 

 tance about the south border of the Drift- 

 less Area. Evidence of complete coales- 

 cence, however, is not decisive so far as yet 

 discovered. 



These developments serve to throw light 

 upon the cause for the scarcitj'- of lacustrine 

 deposits in the Driftless Area. They show 

 that there was at most but a brief period in 

 which the southward drainage of the Drift- 

 less Area was completely obstructed by the 

 ice sheet. 



By means of maps it was brought out 

 that there were probably two centers of ac- 

 cumulation — one, the earlier, toward the 

 northwest; and the other, the later, in the 

 Labradorian heights. In the discussion E. 

 D. Salisbury remarked the great complex- 

 ity of the glacial period, and G. Frederick 

 Wright, while admitting the minor complex- 

 ity, emphasized its essential grand unity. 

 President Shaler called attention to the 

 importance of demonstrating the progress of 

 glaciation from west to east, because if we 

 can establish the sequence of events, we 

 have advanced a long way toward discover- 

 ing their cause. 



The Loess of Western Illinois and Southeastern 

 Iowa. Frank Leverett, Denmark, Iowa. 

 The north border of the loess both in 



