1869.] HUNT — GEOLOGY 01 SOUTH WESTERN ONTARIO. 17 



ancient basins, or geographical depressions in the surface of the 

 underlying formation, in which were deposited these thicker por- 

 tions. The existence of these Upper Silurian salt lakes, whose 

 evaporation gave rise to the rock-salt, gypsum and dolomite of the 

 Salina formation, shows a climate of great dryness to have then 

 prevailed in this region. A similar conclusion is to be drawn 

 from the more or less gypsiferous dolomites of the Calciferous and 

 Niagara formations, the magnesian limestones at other horizons, 

 and the gypsum and salt deposits of the Carboniferous period, — 

 leading us to infer a very limited rain-fall over the north-eastern 

 portion of this continent, throughout the Paleozoic period. 



In this connection, a few remarks with regard to the horizon of 

 the petroleum which issues from the Devonian rocks of Ontario, 

 may not be out of place. In opposition to the generally received 

 view, which supposes the oil to originate from a slow destructive 

 distillation of the black pyroschists belonging to the middle and 

 upper divisions of the Devonian, I have maintained that it exists, 

 ready formed^ in the limestones below.* — In addition to the well 

 known fact of its frequent occurrence in the Corniferous lime- 

 stone, I have cited the observations of Eaton, Hall and myself, 

 as to the existence of both solid and liquid bitumen in the Niagara 

 limestone, and even in the massive beds of the Hamilton. A 

 remarkable example is afforded in the oleiferous beds of the 

 Niagara formation in the vicinity of Chicago, f and still another 

 in similar strata belonging to the Lower Helderberg period, in 

 Gaspe. The deep borings already mentioned in Tilsonburg, St. 

 Mary's and Enniskillen, showed in each case small quantities of 

 petroleum in strtita of the Salina formation, and the same was 

 observed at considerable depths in the Goderich well already 

 described. 



Apart from the chemical objections to the view which supposes 

 the oil to be derived from tlie pyroschists above the Corniferous 

 limestone, it is to be remarked, that all the oil wells of Ontario 

 have been sunk along denuded anticlinals, where, with the excep- 

 tion of the thin black band sometimes met with at the base of the 

 Hamilton formation, these so-called bituminous shales are entirely 

 wanting. The Hamilton formation, moreover, is never oleiferous, 



* Canadian Naturalist, June, 1881 , and Silliman's Journal, March, 1863 

 t It is proposed to give, in a subsequent communication, the results 

 of an examination of this remarkable limestone. 

 Vol. I. C No. 1. 



