506 GEOLOGY OF THE WESTERN DISTRICTS OF CANADA. 
about twenty feet thick, is observed to attain a thickness of one 
hundred feet in Eramosa, Nassagaweya and Caledon. This limestone, 
as well as the underlying Clinton limestone, is everywhere well adapted 
to form an excellent and durable building material, and is likewise of 
good quality for burning into lime. It forms wherever it crops out a 
bold escarpment (which may be called the Niagara ridge) owing to its 
solid and apparently unstratifiea character. This escarpment is 
distinctly traced from West Flamboro’ eastward into Nelson, where it 
takes a sweeping turn to the north, and maintains a nearly straight 
course in that direction until it reaches Owen Sound near Sydenham 
village. The dark bitumimous limestone which forms the upper 
member of the group follows the same course, which, however, is not 
so distinctly marked, owing to its being stratified in thinner beds, and 
occupies throughout from the Niagara River toOwen Sound, a breadth 
of country varying from eighteen to twenty or twenty-two miles. 
The red marl which forms the base of our series of rocks is supposed 
to be about 614 feet thick. The bore which yields the mineral water 
at St. Catherines pierces it for a depth of nearly four hundred and 
seventy feet without passing through it, and the level at which the 
bore commences is one hundred feet below its upper surface. It 
seems geographically to come to an abrupt termination at the west 
bank of the Creek at Oakville, and is there succeeded by the Lorraine 
Shales, or Hudson River Group—an older formation consisting of 
alternate very thin beds of limestone and shale, which extend from 
this point along the north side of Lake Ontario to the River Rouge 
in the township of Pickering, immediately adjoining Scarboro’. A 
good section of this formation is exposed on the east bank of the 
Don at Toronto. A bore which was executed under my directions at 
the Toronto Station of the Great Western Railway, penetrated it for 
a depth of one hundred and fifty feet without change. The water 
which this bore yielded was salt and bitter, and a considerable 
quantity of carburetted hydrogen gas was evolved. 
I may here remark in passing that in the spring of 1855 a great 
land-slide occurred on the slope of the mountain a little below Dundas 
Station, which displaced a portion of the track of the Great Western 
Railway, and was caused by the weight of the debris of the harder 
rocks above sliding along the face of the soft shales which, by exposure 
to the weather, resolve themselves into an unctuous sort of clay. 
may also notice that in filling up the old channel of the Desjardins 
