148 



ROCHESTER ACADEMY OF SCIENCE. 



the rock valley, the\ proceeded to "putty u|)" that valley, at least 

 its deeper part, with their ground-moraine or till ; hut some of the 

 later movement, being more nearly lengthwise of the depression, 

 may have partially cleaned out this earlier filling, though the flow 

 was still somewhat oblique to the valley as late as the formation of 

 the \Mnton Road drumlin. Whatever the explanation, in the end 

 the glacial ])utty fell considerably short of obliterating the valley on 

 the parallel of Rochester, as is shown in Figure 4. 



Figures 4 to 7 Longitudinal Profiles showing Stages of Filling and Re- 

 excavation of the Lower Irondequoit Valley. 



(LA KE D W y/S C i\J J 



Fig. 4. Glacial Filling. Longitudinal profile of the lower Irondequoit valley 

 showing approximate surface of the glacial drift as left by the ice. 

 Vertical exaggeration 17.5. The position assigned to the rock floor of 

 the valley is purely hypothetical ; it is probably deeper than shown rather 

 than less. Lake Dawson waters nearly overtop the vallej' rim. Com- 

 pare Map A (Plate IV) and succeeding figures. 



j\Iore important, therefore, than these local glacial deposits, as 

 concerns the subsequent history, were those made farther south, 

 around Fisher's and ^vlendon, in the form of huge kame-moraines 

 built at the ice margin ; for these determined the actual eviction 

 from this valley of the drainage that formerly followed it. Save 

 for these barriers the Genesee would to-day pass out the Irondequoit 

 jwrtal and little wotild have been si^ared of the present silt plains 

 or similar fillings under the onset of so mighty a stream. Xor coitld 

 Ave write "obit" of the valley, but "etiam vivens". 



So familiar are these facts from the writings of others that we 

 may pass them over thus lightly and return now to the serious 

 contemplation of the aftermath, — the "post mortem" period of our 



