128 ROCHESTER ACADEMY OF SCIENCE. 



farther out by some miles, and the erosion'al capacity of the Ironde- 

 qupit River was greater than to-day. Lake Ontario is readvancing 

 upon its south side, and all the streams entering it here are 

 "drowned" in their lower reaches, none illustrating this better than 

 the Irondequoit and the Genesee. Figure 2 represents these lake 

 levels, which may be summarized thus : — 



Lake Dana _ . - 750 feet above present sea-level 



Pause at - - - - 540 - " " " " 



Lake Dawson (final) - - 480 " " " " " 



Lake Iroquois (final) - 435 



Lake Emmons _ _ - 320 



Lake Vermont^ - - 250 ( ?) " " " " " 



Gilbert Gulf, initial, falling - 175 ( ?) " " " " " 



transition - HO ( ?) 



Lake Ontario, rising to - 247 



The Lake Deposits. 



Earlier lakes. Lake Dana and its 540 foot successor made no 

 distinctive deposits in the lower valley proper, although the influence 

 of the former is very conspicuous in the upper valley from Rail- 

 road Mills to Fisher's.^ Lake Dawson, however, with its outlet via 

 the splendid channel from Fairport to Lyons, left more indelible 

 traces on our maj). Its wavework was here too cramped to build 

 strong spits and bars, but it ate away the declining east end of the 

 Pinnacle kame as far as where the Erie Canal swings around it at 

 Brighton, thus leaving only trains of bare boulders to mark the 

 former extension of that moraine into the re-entrant angle between 

 the Genesee and Irondequoit lobes. From Brighton to Fairport the 

 Dawson shoreline is followed approximately by the Canal, and on 

 the north and east of this shore in the Allen's Creek valley our 

 map shows extensive, but dissected, surfaces at the Dawson wave- 



7. Vermont-Xew York of Fairchild; now regarded by him as a sea-level water body 

 higher and earlier than the Gilbert stage. For the names of this lake and its predecessor 

 Emmons see Bulletin 158 X. Y. State Museum: pp. 33-3.3; for the later interpretations. 

 Bulletin 164: pp. 22-24, also the Bulletin of the Geological Society of America. Vol. 24: 

 pp. 1.37-160 and Vol. 25: pp. 220. 233-242. (All by H. L. Fairchild). 



The question of the nature of Lake Vermont, or even of the higher Emmons and 

 Iroquois, whether sea-level or glacial, in no way affects the conclusions set forth in this 

 paper. 



S. See map, PI. 2. Bulletin 127 X. Y. State Museum. 



