iSm.] 361 [Grabau. 
lateral slrcains. Fall Brook and Beard's Cieeki, entering the 
main valley from opposite sides, measure its width. These 
streams enter through short postglacial goi-ges at the head of 
which are perpendicular falls of sixty feet or more, formed by a 
hard layer of Portage i-ock capping the softer Genesee and 
Moscow shales. The sides of the valley as far as Avon are 
formed by the Genesee, Hamilton, and Marcellus shales, and on 
account of the soft nature of these shales they have been degraded 
to a considerable extent giving the valley its ill-defined outline. 
Near Rochester the river enters upon its course through the 
final portion of its channel which is again a postglacial gorge 
seven miles in length, and cut into the Niagara, Clinton, and 
Medina rocks. In this gorge also are three falls, one at Roches- 
ter, ninety-eight feet high, over the thin lower layer of Niagara 
limestone, another of twenty feet over the Clinton band, and a 
third of one hundred and five feet over the hard, upper Medina 
sandstone. 
Topography of the adjacent region. — An examination of the 
country on both sides of the Genesee reveals the existence of two 
other preglacial valleys, one on each side of the river. (See 
fig. 1.) These are occuj^ied, however, by small streams only. 
The western valley first becomes well defined near Castile. From 
this point northward it grows more and more prominent until for 
several miles south and north of Warsaw, which lies in its center, 
it has the definition, width, and apparent depth, together with 
the flat bottom and drift-covered sides, of the valley south of 
Portageville. The rock is revealed in several lateral gorges near 
Warsaw, and consists mainly of the Portage shales and sandstones. 
Near the center of the valley, rock has been found at a depth of 
from one hundred and fifty to two hundred feet below the valley 
bottom.- The average width of the valley is one mile, which 
corresponds closely with the width of the valley south of Portage- 
ville. The bottom of the valley at Warsaw has an elevation 
appi-oxi mating 1,000 feet A. T., while the top of the hill at the 
Erie Railway station is 1,326 feet A. T., the elevation of Portage 
Station l)eing 1,314 feet. The Oatka, or Allen's Creek, a small 
stream emptying into the Genesee near Scottsville, occujiies the 
' These streams are similar in cliaracter to those entering Cayuga and Seneca Lakes 
through postglacial gorges, at the head of which are falls. 
^ Kindly communicated by Mr. L. E. Lounsberv of Warsaw, N. Y. 
