124 ROCHESTER ACADEMY OF SCIENCE. 



of broader problems involved ;- much of the results having mean- 

 while become public through use in the classroom, and parts having 

 been duplicated or corroborated by advanced students in the college. 



Physiographic Divisions. 



As a physiographic unit, the valley of the Irondequoit heads 

 at Fisher's, fifteen miles by rail southeast from Rochester, where 

 the stream itself enters it from the side (see Key Map, Fig. i). 

 From Fisher's down to Lake Ontario it is divisible into four equal 

 .sections of four and a cjuarter miles each. The first section, from 

 the entry of the headwaters to Bushnell's Basin, is heavily obstructed 

 by kame and esker fillings which divide it more or less continuously 

 into a double depression ; this is the Upper Valley. The second 

 section, from the Erie Canal at Bushnell's Basin to Penfield village, 

 is filled nearly to the brim by a broad silt plain across whose level 

 surface the canal and railroads find favorable passage ; this is the 

 IMiddle Valley. The third is the ''dugway" section," deeply trenched 

 ill these same silt plains and afifording picturesque submountainous 

 scenery ; this section extends from Penfield to the Float Bridge 

 (see Plate III, facing front page). The fourth or "bay" section 

 combines the steep silt bluffs with a lake-like sheet of water laving 

 their base, uninvaded by commerce, that has no peer in our inland 

 waters. This section extends from the Float Bridge to Sea Breeze 

 (Lake Beach of the map), and together with the preceding "dug- 

 way" portion constitutes the Lower Valley, the subject of this paper. 



It is this lower half of the valley, eight and a half miles in 

 length from Penfield to Lake Ontario, that is shown upon our maps. 

 Allen's Creek, the most important Irondequoit tributary, enters at 

 its upper end, issuing from a well-marked minor valley on the 

 sovithwest. Otherwise the lateral drainage of this Lower Valley is 

 exceedingly local. 



Glacial Lake Succession. 



It has been shown by Prof. Fairchild"* that the present surface 

 depression of the Irondequoit is but the shadow of a greater rock- 



2. See references 1)eyoinl to papers on Lakes Vermont and Emmons. 



3. The name "dugway" is locally applied to the three roads carved across this sec- 

 tion of the valley. See Plate III. 



4. See the paper just cited on preceding page. 



