438 A POPULAR EXPOSITION OF THE 
Hunt as more probably due to the contraction of the gypsum masses 
having been less than that of the overlying and contemporaneously 
deposited shale materials, in consequence of which, the latter would 
gradually settle down and fold themselves around the gypsum. An- 
other view assumes the sulphate of lime to have been -riginally 
deposited in the form of anhydrite, a closely related mineral but without 
water of crystallization. The after absorption of water would then 
cause an increase in bulk, and so produce the bulging and fracturing 
of the overlying beds. 
Fossils are scarcely known in this formation. A few obscure and 
rare traces of organic forms are all, indeed, that have been recognized 
in Canadian localities. ‘The Onondaga deposits are in great part of 
chemical origin, and were evidently accumulated in strongly saline 
waters, principally by evaporation: facts which go far to explain the 
absence of organic remains. The only forms of probable occurrence 
would be certain cyproids or bivalve entomostracans, as species of 
these, at the present day, habit brine solutions in which an active 
evaporation is going on. Casts of prismatic crystalline masses, how- 
ever, like that exhibited in figure 214, and others of a flat and square 
pyramidal or hopper-shaped form, the latter evidently derived from 
ordinary salt, are of not uncommon occurrence. This would follow 
naturally from the conditions under which the beds were deposited. 
The Onondaga formation (No. 13 in the sketch-map, fig. 249) crosses 
the Niagara River above and below Grand Island, or a short distance 
above the Falls, and follows the general outcrop of the Niagara and 
Guelph formations up to the vicinity of the Saugeen River on Lake 
Huron. It thus passes through portions of the Counties of Welland, 
Haldimand, Brant, Oxford, (north-east corner), Waterloo, Perth, and 
Bruce, but throughout much of this area it is covered by Drift accu- 
mulations. On the American side of Lake Huron, the picturesque 
island of Mackinaw is chiefly made up of Onondaga rocks, and these 
occur also in places on the adjoining coast of Michigan. Canadian 
exposures are exhibited chiefly near the village of Waterloo, in Bertie 
township, on the Niagara River; along the Grand River between 
Cayuga and Paris, and higher up the stream near the Don Mills; at 
places near Ayton and Newstadt, in the township of Normanby, on 
the Upper Saugeen; around Walkerton, on the Saugeen River, in 
Brant township ; and at various pots down the river, more espe- 
cially at the elbow in the south-west corner of Elderslie township, 
