231 



been invaded by the ice sheet, and at tlie same time tlie draiiia.tre was held 

 up by the interference of the ice slieet at the month of Bean Blossom. 



The evidence of the arrest of drainage at the time of ice invasion is 

 found in the occurrence of a series of benches, inaptly termed terraces by 

 some writers, rimming the eastern and northern slope of the valley at 

 various points within the limit of ^Monroe County and are reported to occur 

 with increased frequency in Bi'own. 



In all the sections and cuts found in tlu> benches, only clay and sandy 

 materials appeared. No limestone and sandstone exposures, such as make 

 up the valley slopes, were found in the benches; their contents are ini- 

 doubtedly made up of tlie wash and sdil-cicc]) bronglit into tlie valley from 

 the uplands, the clay portion being derived from the dcfonipiised lime- 

 stone and the sand constituency from the underlying knob stone. 



The benches vary much both in form, areal extent and elevation al)ove 

 the valley lloor. They are invariably attached to tlie slope, and exhibit in 

 most instances a remarkably tiat or sometimes gently sloping surface 

 towards tlie outer edge. The outer liiii is usuall.v lobale in f(irni. with 

 narrow, youn,g valleys extending towards the rock slopes, and sometimes, 

 so far, as to traverse the entire width of the bench. The slope of the outer 

 edge is usuall.v sreep and well dcliued. In some cases the tops of the 

 benches are slightly undulatin.g or rolling. Those, however, seldom attain 

 the elevation of the tlat-topped ones. In Marion and Washington Town- 

 ships tlie.v ma.v be traced contiiuKnisl.v for three or more miles, and .attain 

 a width of something over half a mile. They also vary much in elevation 

 aliove the valley tioor. attaining a maximum hei.ght in Marion Township, 

 sections I'.i and 20. of seveiit.v or mori' feet, and decreasing graduall.v down 

 stream, until in section 32, Washin.gton, tliey are found to lie some twenty- 

 tive to thirty feet above the valley tioor. 



That these benches must have been deposited in water is attested to 

 by various criteria. The tiat tops, steep angle on the front, and stratitica- 

 tion show that they are delta-like accuinulations brouglit in during tlie 

 arrest of the drainage and not tciraccs in technical sense, .ilthoiigh they 

 appear very much like the latter so far as form is concerned. 



The various elevations attained in different parts of the valley may be 

 due to different levels at wliicli ilu> laked v.-illey stooil during tlie lakin,g 

 period, or it may be accounted for in part, at least, to the larger contribu- 

 tion of residual materials from u])lands to the ui>i)er part of the valley by 

 the nortlicni trilnitaries. tliaii liy similar streams emptying into Bean 



