LAKES. 241 



Should this lake be, as believed, a lake of excavation, this effect was anterior to its present 

 dip, and the period which preceded the change of inclination of its rocks was the one in 

 which the basins of the southern lakes were also formed or excavated. 



Oneida Lake. 



It forms a part of the long and broad level which commences near Utica, and extends through 

 the third district, dividing the counties of Madison and Oswego. Its length is about nineteen 

 miles, and its greatest breadth six miles ; its greatest depth is said not to be over sixty feet. 

 In general it is shoal, and the lake grass or weed may be seen in many parts to a considerable 

 distance from the shore. It has two small islands, which appear to be of alluvial origin. It 

 is excavated in the Clinton group, the rocks of which appear on the south shore, and at the 

 west end. Its north shore is entirely covered with alluvion, which is low at the west end, but 

 rises to a himdred feet towards the east end. The banks of the outlet are low, as well as all 

 that part where it unites with Seneca river. 



This lake is beautifully seated, when viewed from the north side. The gypseous hills rise 

 with rounded outline from the low green border of the lake ; back of which is the more ele- 

 vated range of the Helderberg, upon which the more distant ends of the north and south ranges 

 of the higher rocks appear. 



Onondaga Lake. 



This small but interesting lake is about five miles in length, and about a mile in breadth ; 

 its greatest depth sixty-five feet. It is the remains of an ancient and deep excavation in the 

 Onondaga salt group, of which Onondaga valley forms the southern part ; all which has been 

 filled up with sand, gravel, etc., except the part occupied by the lake. The last boring which 

 was made in the ancient excavation at the head of the lake, extended 265 feet below the 

 surface, vrithout reaching the bottom. The bottom of Onondaga lake and its sides are covered 

 with lake marl, showing a thickness where bored of six and more feet. 



One of the advantages of the survey, has been to throw light upon the salines of Onondaga, 

 showing their true nature, which is now well understood. The ancient excavation of which 

 the lake forms a part, has been filled up with alluvion, forming a reservoir, into which the 

 waters are received which have percolated through the gypseous range, at some distance to 

 the south of their outcrop, and dissolved a portion of the saline materials of that range. The 

 various borings and wells at the salines are connected with the reservoir ; the deeper they 

 have been sunk in the alluvial, the stronger is the water, the marl of the lake insulating the 

 salt water of the reservoir from the fresh water of the lake. 



Geoi,. 3d Dist. 31 



