348 FRA NK B URSLE V TA YL OR 



These considerations disclose the true relation of the Berk- 

 shire ice-tongues to the Hudson lobe. They were absolutely 

 dependent upon that lobe for all their movements, and they 

 reflected its conditions in the most intimate way. They were 

 all parts of the lobe itself and constituted a mere fringe along its 

 border. If Berkshire county had been an even plain, either flat 

 or gently inclined, the border of the lobe would have crossed it 

 in straight lines, and the recessional moraines would have been 

 straight and parallel. There would be no reason, then, to sup- 

 pose dissynchronous movements at different points on the line. 

 The rugged topography has not altered this relation. It pro- 

 duced a fringe of ice-tongues, but those tongues had no dissyn- 

 chronous movements among themselves. They all advanced at 

 one time, they all retreated at one time, and they all halted at 

 one time. 



The conclusion to be drawn from these considerations is that 

 the ice-border at each halt rested on a line which was distinct 

 and separate from the line of the halt that preceded it ; so that 

 if perfectly continuous moraines had been made along the entire 

 margin at each halt, these moraines would now be separate and 

 distinct individuals, extremely sinuous, but still roughly parallel 

 and without any overlappings. Local differences of climate may 

 have produced some slight dissynchronism of movements, and 

 glacial erosion may have added a little to the same result, but 

 the effects attributable to these causes appear to be so small 

 as to be well within the ordinary width of the moraines. Some- 

 times moraines are a mile and one-half to two miles wide, and 

 they are then generally composed of three or four secondary 

 ridges more or less distinct, suggesting waverings or changes in 

 the position of the ice-front during the halt. Border drainage 

 channels often show the same waverings. But whether these 

 very slight waverings were due to general or local causes is not 

 yet clear. 



Alpine glaciers, on the other hand, show widely dissynchro- 

 nous movements.^ While one advances, another retreats, and 



^ H. A. Reid, "Variations of Glaciers," reports in several recent volumes of the 

 Journal of Geology. 



