S Wright — Theory of an Interglacial Suhmergence. 



himself had begun to make at the time of his lamented death. 

 When, in 1880, Professor Lewis conducted the glacial survey 

 of Pennsjdvania with me, we were laboring under the mistaken 

 idea that the margin of the glaciated area was everywhere 

 marked by a pronounced terminal moraine, and we did not 

 pay sufficient attention to the so-called "fringe" of glacial 

 deposits which nearly everywhere extends a greater or less 

 distance in front of the moraine. In my own subsequent 

 work west of Pennsylvania I devoted my main efforts to the 

 determination of the boundary of this fringe, leaving the 

 interior moraines to be tilled at leisure. The correction of our 

 determinations which has been made by Mr. Max Foshay in 

 Western Pennsylvania, and that by Messrs. Salisbury and 

 McGee of Professor Cook's work in New Jersey, had already 

 been foreshadowed both by Professor Lewis and by myself,* 

 but, as we rightly supposed, nowhere in Pennsylvania and 

 New Jersey does the fringe extend many miles south of our 

 moraine. 



In England Professor Lewis's moraine as reported to the 

 British Association needs about the same correction to deter- 

 mine the extreme limits of the ice as is required in Penn- 

 sylvania. Almost everywhere in England there was a fringe 

 of glacial debris in front of Lewis's moraine, but in England 

 no more than in America does it seem to be necessary to 

 interpret this fringe as the remnants of an earlier and distinct 

 glacial period. The close conformity of the boundary of the 

 fringe to that of the more pronounced glacial deposit seems to 

 point clearly to the operation of a common cause ; for it would 

 seem in the highest degree improbable that two distinct glacial 

 periods should so closely correspond in the marginal line of 

 their deposits. Certainly we should not make this supposition 

 except in the presence of facts which will not allow of a sim- 

 pler explanation. 



Oberlin, 0., Oct. 16, 1891. 



* See The Ice Age in North America, pp. 135, 136. 



