LAKE NKWJiKKRY. 4G5 



tude of tlie Ontario basin from 340 to 300 feet lower than now, was lontj; su])se(iuont to 

 the invaj^ion of the Seneea valley by the Warren waters. The duration subseiiuent 

 to this invasion, while the ^lohawk valley was yet iee-buried, but while the area 

 of the Finy;er lakes was relieved of its iee-burden, would probably have allowed the 

 latter area to recover somewhat from its depressit)n.* The relation of the subse- 

 ijuent Inxiuois ])lane to the earlier lifted area would not therefore indicate that 

 previous ui)liftin«j. Only 100 feet of earlier elevation would be required, according 

 to the calculation above, to make the channel an outlet for Warren waters. 



Another reason for believing in the probability of considerable depression in the 

 Seneca-Cayuga region is the pronounced convexity or lobingof the watershed and 

 of the frontal moraine (see plate IS of this volume). This lobing of the ice-front, 

 probably due to the great dei)th of the valleys and massing of the ice, produced 

 a local accunuilation of weight which may possil)ly have caused an excei)tionally 

 great local depression. 



The Horeeheads channel is described in the former paper (pages 3()()-36i)). Con- 

 cerning the smaller breadth of the channel comi>ared with those of the Chicago and 

 the Rome outlets, it may be said that, at the longest, lake Newberry had a rela- 

 tively short existence. However, between the higher tlood-})lains the channel is 

 (piite a mile l)road. 



In all the local lake ])asins, so far as observed by the writer, the heaviest delta 

 terraces are at the summits of the deltas, corresponding to the local outlets, and 

 not at the supposed plane of lake Newberry. The absence of extremely heavy 

 delta accumulations at the supjwsed proper level suggests several replies : 



Firet. The size of a delta depends not at all upon the size of the receiving water 

 body, but upon the volume of detritus borne in by the stream, multii>lied by the 

 length of time. The uni>rotected drift left by the ice-sheet was accunmlated in 

 deltas very rai)idly by the earliest streams. As the lake level fell the streams 

 simply bisected their deltas and contributed to lower levels only the regular, re- 

 duced sujjply. 



Second. The local lakes had a steadier level and more uniform conditions than 

 the continental lakes, with their vast areas and differential movements of outlets 

 and distant shores; an<l the duration of some of the local glacial lakes was con- 

 siderable. 



Third. In the case of the non-existence of lake Newberry, then the shore in- 

 scriptions of the Warren waters must be found in all the valleys of central New 

 York at a present elevation not far below UOO feet, unless there was, as mentioned 

 alMjve, some unsus|)ected (jutlet. However, there seems to be, so far as observation 

 now extends, no good evidence of a general water-level below 1)00 feet, while from 

 Batiivia eastward the lower terraces (jf stream deltas d(j suggest a general water- 

 plane near <jr al)Ove 900 feet. 



Fourth. Similar absence of shore-markings is freijuent about the shores of the 

 great glacial lakes. 



" MoHt of the n<»rtliorn l»e!wl>es (of liiko Wjirrcn), it should l)e remaikcd, aro very feeldy de- 

 veloped, even In tlie most favorable situations for tlioir formations, and am not disccrniljle along 

 the far greater part of the lake borders." f 



The writer suggests the possibility, as hel|)ing to explain the want of strong shore 

 phenomena, that lake Newberry may liave had a brief ami precarious existence, 



• Wurren Upham : Wave-like progresH of an epeirogenic uplift. Journal of Geology, vol. ii, pp. 

 .383-395. 

 t W'urreu Uphum : Am, Jour. Sci., January, lbu5, p. 7. 



