308 ANNUAL OF SCIENTIFIC DISCOVERY. 



of alternations of limestone and softer strata, the rocks have been worn by 

 denudation into a succession of terraces, the chief of these forming a great 

 escarpment, part of which, by the river Niagara, overlooks Queenstown and 

 Lewiston, and, capped by the Niagara limestone, extends from the neigh- 

 borhood of the Hudson to Lake Huron. Divided by this escarpment, the 

 plains of Canada bordering the lakes, and part of the United States, thus 

 consist of two great plateaus, in the lower of which lies Lake Ontario, Lake 

 Krie lying in a slight depression in the upper plane or table land, 329 feet 

 above Lake Ontario. The lower plain consists mostly of Lower Silurian 

 rocks, bounded on the north by the metamorphic hills of the Laurentine 

 chain. The upper plain is formed chiefly of Upper Silurian and Devonian 

 strata. East of the Hudson, the Lower Silurian rocks that form the lower 

 plain of Canada become gradually much disturbed and metamorphosed, and 

 at length, rising into bold hills trending north and south, form in the Green 

 Mountains part of the chain that stretches from the southern extremity of 

 the Appalachian mountains to Gaspe, on the Gulf of St. Lawrence. Be- 

 tween the plains of the lakes and this range, the steep-terraced mass of the 

 Catskills, formed of old red sandstone, lies above the Devonian rocks facing 

 east and north in a grand escarpment. The whole of America south of the 

 lakes, as far as latitude 40, is covered with glacial drift, consisting of sand, 

 gravel, and clay, with boulders, many of which, during the submergence of 

 the country, have been transported by ice several hundred miles from the 

 Laurentine chain. Many of these are striated and scratched in a manner 

 familiar to those conversant with glacial phenomena. When stripped of 

 drift, all the underlying rocks are evidently ice-smoothed and striated, the 

 striation generally running more or less from north to south, indicating the 

 direction of the ice-drift during the submergence of the country at the gla- 

 cial period. The banks of the St. Lawrence near Brockville, and all the 

 Thousand Islands, have been rounded and moutonne by glacial abrasion dur- 

 ing the drift period. The submergence of the country was gradual, and the 

 depth it attained is partly indicated in the east flank of the Catskill moun- 

 tains. This range, near Catskill, runs north and south, about ten or twelve 

 miles from the right bank of the Hudson. The undulating ground between 

 the river and the mountains is seen to be covered with striations wherever 

 the drift has been removed. These have a north and south direction ; and 

 ascending the mountains to Mountain House, the speaker observed that 

 their flanks are marked by frequent grooves and glacial scratches, running, 

 not down hill, as they would do if they had been produced by glaciers, but 

 north and south horizontally along the slopes, in a manner that might have 

 been produced by bergs grating along the coast during submergence. These 

 striations were observed to reach the height of 2,850 feet above the sea. In 

 the gorge, where the hotel stands at that height, they turn sharply round, 

 trending nearly east and west; as if, at a certain period of submergence, 

 the floating ice had been at liberty to pass across its ordinary course in a 

 strait between two islands. During the greatest amount of submergence of 

 the country, the glacial sea in the valley of the Hudson must have been be- 

 tween 3,000 and 4,000 feet deep, and it is probable that even the highest tops 

 of the Catskills lie below the water. In Wales, it has been shown that during 

 the emergence of the country in the glacial epoch, the drift, in some cases, 

 was ploughed out of the valleys by glaciers ; but, though the Catskill moun- 

 tains are equally high, in the valleys beyond the great eastern escarpment 

 the drift still exists, which would not have been the case had glaciers filled 



