QUATERNARY DEPOSITS. 219 



Pratt's-Hollow. In Onondaga valley there are two deposits, one on the Indian reservation near 

 the mouth of South-Onondaga valley ; there the hills are highest, and the accumulation the 

 greatest, some of the hill appearing to be over one hundred feet in height : the other is a lesser 

 deposit, and near the head of the valley. A similar but smaller deposit exists at the head of 

 Otisco valley, near where the road takes a rise into the valley which leads to Homer ; also 

 another in the head of the valley which extends south from Skaneateles lake, in the town of 

 Scott. The last great deposit is in Cayuta creek at the head of Cajmga lake, and extends 

 for miles along the creek. 



Some of these deposits greatly resemble the hills of loose materials which rise in the valley 

 near Fall and Cascadilla creeks, near Ithaca. The hills appear to have been formed by the 

 waters of the creeks when the lake was at a higher level ; for where such substances are de- 

 posited in deep and tranquil waters, there is no tendency to diffusion ; the head of the lake 

 upon which Ithaca is seated, being a perfect flat. 



There are numerous points where the alluvial appears to have been formed over the hill 

 side, besides those near the mouths of the creeks near Ithaca ; such is the mass on the west 

 of Onondaga village ; the descent into the valley northwest of Waterville ; north of the village 

 of Greene in the Chenango valley, etc. etc. 



These deposits of alluvion near the line of dividing waters, greatly resemble certain accu- 

 mulations of similar deposits noticed in the survey of Massachusetts, called diluvial elevations. 



The whole of the district south of the north line of the Helderberg range, shows an im- 

 mense accumulation of alluvial deposits, either filling up the valleys and forming level surfaces, 

 or ranging by the sides of the valleys as terraces, or thrown into irregular hills in the valleys, 

 and also occurring on the heights apparently in no regular order. The deposits consist of 

 rolled stones large and small, sand, clay and earth. The rolled stones are in prodigious amount, 

 nearly two-thirds of which are from rocks north of the Helderberg range. They consist 

 chiefly of primary rock, and grey and red sandstone. In some locaUties, those of limestone 

 are numerous ; and where they exist, as their gravel and soil are often present, they give rise 

 to deposits of tufa or lake marl ; the former kind if air only be present, the latter if deposited 

 in water. 



The excavation of the Chenango canal from Oriakany falls south is entirely in alluvial ma- 

 terials ; showing frequently, in the northern part of the town of Madison, a mass of gravel 

 and large rolled stones as an upper deposit. Below the rolled stone, there is often a deposit 

 of blackish or dark-colored sand, fine or coarse, which is the common sand of the whole of 

 the south valleys. The lighter colored sands exist, but are rare comparatively. The lower 

 part of the canal at Chenango forks was in a sand of the kind ; above which was a mass of 

 coarse gravel from six to eight feet thick, with rolled stones from one to eight inches in diame- 

 ter, having on the top finer gravel with thin layers of sand. 



The clays in that part of the district are usually of a lighter color than those of the Mohawk : 

 the dark ones exist, but are rare. Small pebbles of limestone appear to exist also in the 

 clay, as at South-Norwich ; some of the bricks are apt to burst and crumble after being burnt 

 and exposed to the weather, showing the northern origin of at least a portion of its materials. 



