T. C. Chamber lin — Diversity of the Glacial Period. 185 



1. A drift sheet bordered by a terminal moraine attended by 

 scattered drift on its outside formed at the same time as the 

 moraine by minor incidental action. This scattered drift may 

 not inaptly be called a "fringe." It is a trivial phenomenon, 

 a mere incident of the main action. 



2. A drift sheet that, in contrast with the above, thins out 

 gradually to an attenuated edge. A specific example of this, 

 described in detail, may be found in the Sixth Annual Rep. U. 

 S. Geol. Surv., p. 265. There may be scattered incidental 

 drift on the border of this as well as of the moraine. 



3. A bordering tract of scattered bowlders, sometimes reach- 

 ing out many miles beyond any continuous drift. The origin 

 of this is not certainly known, but it is probably due to tem- 

 porary bordering lakes or glacial floods. It is well developed 

 at some points in Dakota and Montana. 



4. A bordering tract of scattered pebbles attended by silt. 

 This is probably due to glacial waters acting at low gradients 

 in conjunction with detached ice, perhaps local, perhaps glacier 

 derived. An example of this is described in detail and dis- 

 cussed in the paper above cited (p. 271.) 



To confound all these and to merge them under a single 

 term is to push science backward. It is especially unfortunate 

 to create confusion respecting the vital distinction between a 

 moraine-bordered sheet with incidental drift scattered outside, 

 and a thin-edged sheet that may be attended by similar scattered 

 drift. The scattered bordering drift is trivial in significance 

 in either case. This is especially so when the terminal action 

 is strong and vigorous, expressing itself in a definite moraine 

 and when the outer drainage is free. The attenuated edge, 

 as distinguished from the moraine-thickened edge, has a radi- 

 cal significance, because it expresses a vital distinction in mode 

 of action. If the term " fringe " had been confined to the 

 first class of phenomena, and the phenomena discriminated 

 with reasonable accuracy, its introduction might prove a con- 

 venience. But the attempt to make it a synonym with the 

 "attenuated border" which happens to be the form the old 

 drift sheets assume, and the failure to distinguish the two 

 phenomena has made its introduction most unfortunate and 

 renders the propriety of its farther use very questionable. 

 The more important phenomena outside the Pennsylvania 

 terminal moraine to which the term "fringe" has been applied 

 I think has been demonstrated to be the border of an older 

 drift sheet, and not at all a "fringe" of the terminal moraine 

 with which it has no genetic connection. 



Turning to the phenomena of the Delaware Valley, it will 

 assist to a clear understanding of the question if it be recalled 

 that in the original mapping of the drift of the region by the 



