GLACIAL WATERS IN CENTRAL NEW YORK 49 



and South Onondaga district (as moraine drift is probably buried 

 in these latter deltas special care may be necessary here). 



His diagnosis will begin with the most obtrusive feature, the 

 exceeding stony character of the fields. Perhaps the boulders 

 are so large and so abundant that the surface has not been put 

 under cultivation, like much of the delta opposite the Railroad 

 channel. If the ground has been plowed then stone walls or fences 

 (often a superfluous number) will likely be seen, and perhaps 

 cairns or piles of the unused cobbles. Closer observation will 

 reveal some degree, of uniformity in the size of the stones in a 

 restricted locality; also that they are more rounded than the ordi- 

 nary stones from drift. In most of the deltas cited there is a 

 decided preponderance of limestone, with only a small percentage 

 of foreign material. 



Noting the general form of the deposit, it will be found (if it has 

 not been affected by subsequent erosion) to have a generally level 

 or moderately undulating surface, quite unlike a morainic mass. 

 In case of extremely coarse materials the delta plain might not be 

 well developed, and erosion is possible in any case, though this pro- 

 duces terraces or gullies and never kettles. Toward the valley side 

 terraces may be found with steep frontal slopes and smooth, curv- 

 ing horizontal lines, natural to stream erosion. Rarely on the 

 north side of a delta the banks may be found very irregular, having 

 been banked against the ice front, and so exhibiting the unusual 

 constructional form of the " ice-contact." 



If the position, altitude and material be referred to surrounding 

 topography and characters, it will surely be found that the deposit 

 has relation to some stream channel on the west. It may be some 

 distance beyond the mouth of the channel, or near the mouth, or 

 possibly alongside the channel which has cut through or past the 

 delta. The altitude may not have close relation to the producing or 

 inflow channel, but more likely to some outlet channel eastward, and 

 possibly miles away, which determined the level of the lake waters. 



In some cases of deltas of wide extent, kettles or basins may be 

 found, which are best explained by the melting of buried ice blocks ; 

 it being supposed that in the waning of the quiescent ice front de- 

 tached blocks of the stagnant ice, even of great size, might be some- 

 times buried in the massive stream deposits. 



Usually deltas are readily distinguished by their correlation to 

 the producing channel, but sometimes careful discrimination is 

 required. The element most likely to be uncertain is the limits, 



