tS THE CANADIAN NATURALIST. [Vol. vi. 



595 feet of limestone and dolomite were penetrated, without 

 encountering shales ; while in another well, near the last, soft 

 shaly strata were met with at about 600 feet from the top of the 

 Corniferous limestone, there overlaid by the Hamilton shales. It 

 thus appears that the united thickness of the Corniferous forma- 

 tion and the solid limestones and dolomites which compose the 

 upper part of the Onondaga formation, is about 600 feet in Lon- 

 don and Enniskillen, and farther eastward, in Tilsonburg and St. 

 Mary's, considerably greater ; exceeding by an unknown amount 

 in these localities, 854 and 700 feet. 



As the few observations which we as yet possess of the thickness 

 of the Corniferous limestone in this region, do not warrant us in 

 assigning to it a thickness of over 200 feet, it is evident that at 

 London and in Enniskillen the hard strata which form the upper 

 portion of the Onondaga formation, and have at Goderich a thick- 

 ness of not less than 775 feet, are greatly reduced in thickness, 

 since the volume of the two united is only 600 feet. To the 

 south-eastward, however, the augmented thickness of the Onon- 

 daga would appear, from the results of the borings at St. Mary's 

 and Tilsonburg, to be maintained. The thickness of this forma- 

 tion is, however, known to be very variable ; while at the Niagara 

 river it is reduced to 300 feet, and is apparently destitute of salt, 

 it augments to the eastward, in central New York, where it again 

 attains a volume of from 700 to 1000 feet, being equal to that 

 observed at Goderich, and becomes once more salt-bearing. The 

 increased thickness of the formation, in these two regions, con- 

 nected with accumulations of salt at its base, would seem to point 

 to ancient basins or geographical depressions in the surface of the 

 underlying formation, in which were deposited these thicker por- 

 tions. 



Most of the details here given with regard to the thickness and 

 character of the rocks of this region are condensed from the ob - 

 servations collected in my Report for 1866, pp. 241-250. They 

 are embodied in a paper by me entitled Notes on the Geology of 

 South-western Ontario, and published in the American Journal 

 of Science for November, 1868; parts of which have been re- 

 printed, with some few changes, in the last three pages* 



It is a curious fact that the numerous and productive salt wells 

 of Syracuse, New York, although occurring upon the outcrop of 

 the Onondaga formation, do not penetrate into it, but are sunk in 

 a deposit of stratified sand and gravel, which fills up a valley of 



