160 MINERALS AND GEOLOGY 



wood escarpment, for example, we find strata containing marine 

 fossils at an elevation of over 1,500 feet above the sea ; and on the 

 Montreal mountain, shells of existing species occur at an elevation of 

 about 500 feet. Hence, if these strata had been left dry land by the 

 sinking of the oceanic waters in which they were deposited, an 

 immense body of water, extending over the whole globe, must in 

 some unaccountable manner have been caused wholly to disappear. 

 It is therefore now universally admitted, that the sedimentary rocks, 

 as a rule, have come into their present positions, not by the sinking 

 and retiring of the sea, but by the actual elevation of the land. 



Many strata afford proofs of having been elevated and depressed 

 above and beneath the sea, successively, at different intervals. 

 Many sandstones, for example, exhibit ripple-marked surfaces, and 

 occasionally impressions of reptilian and other tracks, throughout 

 their entire thickness. This indicates plainly that they were formed 

 slowly in shallow water, and that they were left dry, or nearly so, 

 between the tides. And it indicates, further, that the shore on 

 which they were deposited, layer by layer, was undergoing a slow 

 and continual movement of depression : otherwise the process of 

 formation would necessarily have ceased, and the strata would 

 present a thickness of a few inches only, or of a few feet at most. 

 Afterwards a period of upheaval must have commenced, bringing up 

 the rocks to their present level. In certain strata, also, the upright 

 stems of fossil trees occur at various levels ; and in some localities, 

 beds containing marine fossils are over-laid by others holding lacus- 

 trine or fresh-water species ; and these again by others with marine 

 remains. Finally, to bring this section to a close, we have a striking 

 example of alternations of land-upheaval and depression in the 

 geology of Canada generally. Around Toronto, for example, we 

 have certain strata of old date, belonging to the Lower Silurian 

 Series, overlaid by deposits of clay, gravel, and sand of the Drift 

 Epoch, a comparatively modern period. Between the two, a vast 

 break in the geological scale occurs. Many intervening formations, 

 indicating the lapse of long periods of time, are present in other parts 

 of this continent; and hence, it is concluded that the Silurian 

 deposits of this locality, after their elevation above the sea, remained 

 dry land for many ages, whilst the intervening groups were under 

 process of deposition in other spots ; and that, finally, at the com- 



