EVOLUTIOX OF IRONDEOUOIT VALLEY. 129 



base level. The region southeast of "Allen Creek" along either fork 

 of East Avenne and northward to the railway is a sand desert whose 

 summits are mostly within the 480' contour — only one small knoll 

 near Pitts ford (not on oin^ map) going above 500'. The original 

 form and extent of these deposits have been obscured by windwork 

 still in progress, to which their irregularity of surface is palpably 

 due. but standing as they do isolated in the midst of the valley, 

 approximately in line with the buried esker described beyond (sec 

 page 143) , it seems reasonable to view them as the pro-glacial delta 

 sands (esker fans) of the Dawson stage. The excess of fine 

 materials is remarkable, yet coarse gravels and even cobble beds 

 occur in the heart of the mass and it is to be noted in this connection 

 that fine sand predominates in the great Turk Hill kame-area onlv 

 six miles southeast from here u]) the same valley. The above inter- 

 pretation requires that the ice front be deeply lobed into this valley, 

 since it must escape the Pinnacle Range at Brighton, but this ar- 

 rangement, which is to be expected a priori, is strongly suggested by 

 the attitude of the deposits themselves. Finally there is a possibility 

 that some of these sand heaps were built upon an ephemeral founda- 

 tion of stagnant ice to which they owe some of their present irregu- 

 larity. Lake Dawson wavework aj^pears again in the low blufif east 

 of Culver Road at East ]\Iain St., just north of the new athletic 

 field. The rest of its shore line through the city shows but weak 

 vestiges of wave action. 



Outer bar or "Ridge Road" of Iroquois. That feature of the 

 Iroquois shore that has attracted the widest attention hitherto is 

 the outer bar or barrier beach known throughout its length as the 

 "Ridge" (or "Little Ridge" in contrast with the adjacent Niagara 

 scarp) and everywhere threaded by a "ridge road". C)n our map 

 it is bounded by the 440 contour east of the bay and by the 420 

 contour on the west. Beyond the Genesee it again exceeds 440 feet. 

 The section north of the city is boldly divorced from the mainland 

 and is often a multii)le bar with minor flanking swells, as specially 

 noticeable east and west of Portland Avenue. But the "ridge" is 

 not always independent of the (former) mainland; at times it gives 

 place to low wave-cut bluffs, as for example at the east edge of our 

 map and again toward the western limit of the Rochester quadrangle 



