162 RALPH S. TARR 



Soils Bureau of the U. S. Agricultural Department recognized this 

 peculiarity, and in mapping the soils of the Elmira Sheet correlated 

 the upland till with a type of residual soil under the name of Hagers- 

 town shale loam. 



This residually decayed material is not confined to a small area, 

 but has been found in the mapping of glacial deposits on eight topo- 

 graphic sheets, and it is certain that throughout this area there has 

 been such slight glacial erosion that in many places, even where 

 conditions seem favorable, the residually decayed products were not 

 removed by the Wisconsin ice-sheet. Whether this is preglacial 

 or interglacial decay is not certain; but so far no facts have been 

 discovered in this region to prove an earlier ice-advance. 



It is true that this is a region in which the length of ice-occupation 

 was relatively brief, and in which the hilly topography was opposed 

 to vigorous ice-action. But even under these conditions it is a signifi- 

 cant fact that ice could have moved over it and have advanced 50 

 miles beyond it, building a traceable terminal moraine, and yet leave 

 so much decayed rock even in exposed places, like hilltops and stoss 

 slopes. 



THE CAYUGA VALLEY 



At Portland quarry, about 6 miles north of Ithaca on the east side 

 of Cayuga Lake, the excavations for the removal of the Tully lime- 

 stone have revealed a condition of profound decay. By this decay 

 the upper layer of limestone has been separated into rounded blocks, 

 with a reddish residual clay occupying the spaces between them, both 

 along the vertical joint planes and along the nearly horizontal stratifi- 

 cation plane between the two upper layers. The decay extends from 

 2 to 3 feet below the surface, and the residual clay is several inches 

 thick. Delicate glacial striae are still perfectly preserved on the sur- 

 face of limestone blocks between and beneath which this residual 

 clay occurs. 



The depth and extent of this decay, together with the evidence of 

 slight postglacial decay furnished by the glacial striae, demonstrate 

 that this residual clay was formed before the advance of the Wiscon- 

 sin ice-sheet, and- that in this place the erosion by the last ice-sheet 

 was insufficient to remove the products of earlier decay. The site of 

 this quarry, near the junction of Salmon Creek and Cayuga Lake on 



