46 NEW YORK STATE MUSEUM 



glacial agents. The gulf canyon is mostly cut in Marcellus shale 

 and the clay detritus has been swept far on toward, or into, the 

 Oneida lowland. 



The Gulf delta is an excellent illustration of the excavating and 

 terracing work of the river on its own deposits, produced by the 

 lowering of its base level, as the eastern channels drained the lake 

 waters. 



Onondaga valley. The massive deposits of the Cedarvale- South 

 Onondaga delta have already been described at some length [p. 28]. 

 The delta tract as mapped would indicate an extent and volume of 

 detritus beyond the amount of rock excavation suggested by the 

 Marcellus gorge, specially as the latter is in shale. It seems proba- 

 ble that beneath the river deposits is considerable volume of glacial 

 (moraine and kame) drift which the ice sheet left in the broad 

 valley lying transverse to the ice movement ; and possibly some of 

 the broad terraces are partly erosional in drift instead of entirely 

 constructional from stream detritus. 



These great deltas were carved and reshaped by their own wate 

 but they seem to have much the forms with which the glacial 

 waters left them, as subsequent activities have modified them but 

 little. They are so vast and varied that some student of the 

 district will find them an interesting and profitable subject for 

 detailed work. 



The many and conspicuous channels in the Split Rock district 

 and west of Syracuse have little delta, apparently, to show for 

 their work, the reasons being manifold. The upper channels are 

 on the limestones and did not cut deeply. The lower channels are 

 in Salina shales which do not contribute delta stuff. The west wall 

 of the Onondaga valley is too steep to afford good lodgment. The 

 coarse and heavy detritus was carried down to the bottom of the 

 deep valley and the later, finer detritus spread over it. The valley 

 lies at a low altitude and was occupied by Iroquois waters, and 

 opening broadly to the north the wave work might have been effec- 

 tive below about 440 feet. The Onondaga creek has long been 

 effective as a distributor of the low-lying detritus. It is probable 

 that the silt from the South Onondaga delta and most of the 

 detritus from the Onondaga HilL Elmwood Park and Split Rock 

 channels has been swept into the valley bottom to make the 

 extended plain on which stands the city of Syracuse The low 

 grounds in the district of Onondaga lake must have a veneer of 

 stream detritus over the sdacial drift. 



