38 



SCIENCE 



[N. S. Vol. XLVI. No. 1176 



beyond. In deference to others we had no 

 objection to substituting the words " atten- 

 uated border " for the word we had selected. 

 The only person who has studied this " atten- 

 uated border " comprehensibly and in detail, 

 in Pennsylvania, is Dr. E. H. Williams, Jr., 

 whose attention was called to the problem 

 twenty-five years ago, while he was lecturer 

 on mining and geology, at Bethlehem. 



By good fortune Bethlehem is almost 

 exactly on the exterior limit of this atten- 

 uated border; and Dr. Williams' familiarity 

 with the mineralogy of the region and with 

 the many problems connected with the work 

 of mining engineering, specially fitted him 

 for prosecuting the investigations which he 

 began and pursued at his own expense until 

 the work was completed. Though many of 

 the results of this work had been presented 

 in piecemeal in various publications, it is 

 only now that they are published in complete 

 form and with adequate description and illus- 

 trations, of which there are no less than fifty- 

 six, mostly photographic reproductions. 



Following the example of Professor Cham- 

 berlin, who first gave a satisfactory explana- 

 tion of the lobate character of the moraines 

 west of Pennsylvania, in the topography of 

 the region. Dr. Williams has brought to light 

 as never before the causes operating to direct 

 and limit the movements of the ice over the 

 mountainous regions of New England and 

 the Middle States. 



1. There was a lobe extending southward 

 between the Green Mountains and the Adi- 

 rondacks through the Hudson Valley, the rock 

 floor of which, between Lake Champlain and 

 the Hudson Piver, was only 150 feet above 

 tide. The average breadth of the upper Hud- 

 son Valley between the 500-foot contour is 

 sixteen miles. Between the 1,000-foot con- 

 tours it is thirty-two miles; but at South 

 Kingston, Ifew York, Storm-King and Marl- 

 borough Mountains rise abruptly 1,200 feet 

 above the valley with a gorge between them, 

 through which the river flows, only three 

 fifths of a mile broad at the 500-foot contour 

 and two miles at 1,000 feet. As a consequence 

 the ice stream was diverted to the southwest 



through the Walkill-Eondout saddle into the 

 great Pennsylvania valley, extending as far 

 as Bethlehem, and damming up the Lehigh 

 Valley so that the outflow of the drainage 

 was turned over the watershed between the 

 Lehigh and the Schuylkill at Topton; thus 

 accounting for the glacial drift, which had 

 been recognized by Salisbury, in the Schuyl- 

 kill River at Norristown. 



A natural explanation of the northwest 

 trend of the glacial border, as shown in east- 

 ern and middle Pennsylvania, is found in the 

 gradual rise of land to the west, which in 

 Potter County attains an elevation of 2,500 

 feet. But in Schuylkill County the swelling 

 mass of ice surrounding and finally over- 

 topping the Catskill Mountains penetrated to 

 Morea a few miles north of Pottsville leaving 

 glacial markings of great interest on the sur- 

 face of the manunoth coal bed, at an elevation 

 of 2,100 feet above tide. 



Again, as the Labrador ice advanced and 

 increased in volimie, passing around the ele- 

 vation of the Adirondack Mountains it pen- 

 etrated the Mohawk Valley through the 

 Black River sag and entered the east fork 

 of the Susquehanna, reaching the valley of 

 the West branch at Williamsport and crossing 

 over it so as to produce a dam causing the 

 water to extend up Eagle Valley and run over 

 into the Juniata at Tyrone, thus accovmting 

 for the glacial debris that I. C. White had 

 found in the lower Juniata. 



But it is in northwestern Pennsylvania 

 that most interesting facts come to light. It 

 appears that there was a long interval after 

 the Kewatin and the Labrador glaciers set 

 out ujwn their careers before they became 

 confluent; so that when the Kewatin ice in- 

 vaded the valley of the Great Lakes and 

 poured its torrential drainage into that valley, 

 Labrador ice was obstructing the eastward 

 exits both through the St. Lawrence and 

 through the Mohawk. This caused a rise of 

 water over the basin of western Ontario and 

 western New York, until, through the Cone- 

 wango, it eventually found an exit into the 

 Allegheny Valley, which then was not con- 

 tinuous but was separated by a col somewhat 



