No. 275. J 243 
over the level we have the continuation of the great elevation of Herki- 
mer and other counties to the east, its line of continuity much broken 
in its progress through the Third District, owing to numerous streams of 
water flowing from the south. To the west and north the limits of the 
level lie not far from a line passing from the north of Rome through 
Salmon creek, in Oswego county. 
The area included within the limits mentioned, presents no elevation 
excepting those formed by alluvial materials only, if we except the 
plaster hills which skirt the northern side of the great elevation, and a 
few other limited projections of the same great mass. The alluvi- 
al materials abound more within this area than in any other part of the 
Third District, consisting of clay, sand, gravel and larger stones, either 
filling up excavations, some at least 200 feet in depth, or rising into 
hills and ridges. 
The area occupies a portion of Oneida, the northern parts of Madi- 
son, Onondaga and Cayuga, and the whole west and south portion of 
Oswego county. 
Were the whole of this ancient level or area stripped of its alluvial ma- 
terials, we should find that the surface presented a lake bottom, appear- 
ing as though Ontario and Oneida once had a higher level, their waters 
uniting and covering the whole surface. That this level or area has been 
the theatre of great erosive action is evident from many facts collected in 
the progress of the survey, facts all important to a right understanding 
of the salines of Onondaga; all which subsequently will be given. 
In Herkimer the great southern elevation consists, as was mentioned 
in the second report, of the green shales, the "millstone grit," the pro- 
tean group, the red shale, the water limes, the upper limestones and 
the " pyritiferous rocks." All the lower, or first named ones, appear 
merely as outcrops, forming as it were the south wall of the valley, 
their northern ends alone to be observed with such other parts as the 
small valleys or ravines which have been excavated in them have ex- 
posed. From beneath these rocks the black shale appears, and forms 
the bottom of the valley. 
The elevation in its progress through Oneida, in consequence of the 
dip of its rocks to the southwest, the rise of the valley and the lower 
rocks rising and passing abruptly to the north from the influence of the 
great primary mass to the north and east, causes the green shale to ap- 
pear in the area and gradually take the place of the black shale. This 
