Febeuaey 21, 1913] 



SCIENCE 



291 



treat are as j'et a matter of interesting 

 speculation. One further difference may be 

 noted between the ice-advance and the ice- 

 recession lakes. The primitive lakes of the 

 ice advance were the lowest in altitude and 

 the most northerly in location and with the 

 lowest outlets. As the ice advanced and 

 closed the outlets the waters were lifted to 

 higher levels and pushed southward. The 

 last lakes of the ice advance being in the 

 heads of the valleys were the smallest, the 

 highest, the most detached and most south- 

 erly. The lakes of ice-front recession had 

 precisely the opposite history. 



Erosional Work. — The lake features that 

 are preserved for our study may be dis- 

 criminated as erosional and constructional. 

 The erosion phenomena are the wave-cut 

 cliffs. The glacial lakes were commonly too 

 ephemeral or too unsteady in their levels 

 to produce conspicuous erosion featiires. 

 However, the larger and longer-lived lakes, 

 as Newberry, Warren, Dana and specially 

 Iroquois, have left many cliffs. 



Constructional Work. — Beach Ridges, 

 embanlanents of sand and gravel, the bars 

 and spits of wave and shore current con- 

 struction, are the complement of the ero- 

 sion work but are much more common and 

 are freqaently very prominent features. 

 They have long been recognized by the 

 people as the work of mysterious waters at 

 high altitudes. For long stretches the 

 beach ridges have been utilized for "ridge 

 roads," while the level stretches of wave- 

 base along the beaches have afforded 

 graded paths for railroads and canals. 

 The strongest ridges are those of Whittle- 

 sey and Warren in the Erie basin, and of 

 Iroquois in the Ontario basin. 



Deltas: Of the several shore phenomena 

 deltas are the most useful in proving the 

 former presence and determining the alti- 

 tudes of the extinct lakes. The production 

 and size of the delta deposits are not wholly 



conditioned by the size of the receiving 

 water body, but by the volume of the 

 stream detritus relative to the distributing 

 work of the receiving waters. Hence deltas 

 may be built in small lakes, and these 

 hung-up mounds and terraces of gravel on 

 the valley sides serve well to mark the 

 shores of lakes that were too ephemeral or 

 too small to produce either cliffs or bars. 

 Naturally the deltas occur in the courses of 

 land streams, and a vertical succession of 

 bisected delta terraces commonly indicate 

 the falling levels of the lake. Fine ex- 

 amples of these gravel terraces are found 

 on the slopes of the Finger lakes valleys and 

 some of them are conspicuous features, like 

 the terraces by Coy glen, visible from the 

 Cornell University campus. 



Delta Plains: Genetically related to 

 deltas are the plains of gravel, sand or 

 clay which may be extended in area and 

 indefinite in limits. Such plains usually 

 represent wave-base, perhaps twenty feet 

 or less beneath the water surface. Wlien 

 partially eroded the remnants present ex- 

 tended horizontal lines, excellent examples 

 of which may be seen throughout the Mo- 

 hawk Valley and about the Irondequoit 

 Valley east of Rochester, clearly visible 

 from the trains on the New York Central 

 Railroad. Some of the larger valleys de- 

 clining toward Lake Erie exhibit broad 

 terraces at various levels. A fine display 

 may be seen from the Pennsylvania Rail- 

 road from East Aurora up to Machias. 

 Evidently such lake plains can occur only 

 north of the divide. Some plains similar 

 in appearance in the valleys south of the 

 divide fall into the categories of outwash 

 plains or of river flood plains. 



Scores of examples of detrital plains 

 built in glacial waters by the land drain- 

 age might be cited. In the Erie basin the 

 great plain in the Cattaraugus Valley be- 

 low Gowanda and that built by Silver and 



