84

ACTION OF ICEBERGS.

CHAP. XIX.

fectly vertical. The submerged portions of such islands must, according to the weight of ice relatively to sea-water, be from six to eight times more considerable than the part which is visible, so that the mechanical power they may have exerted when fairly set in motion must be prodigious.*

To return to the succession of geological changes which immediately preceded the present period in the Niagara district :-Thirdly, after the surface of the rocks had been smoothed and grated upon by the passage of innumerable icebergs, the clay, gravel, and sand of the drift were deposited, and occasionally fragments of rock, both large and small, which has been frozen into glaciers, or taken up by coast ice, were dropped here and there at random over the bottom of the ocean, wherever they happened to be detached from the melting ice. During this period of submergence, the valleys in the ancient rocks were filled up with drift, with which the whole surface of the country was over-spread. Finally; the period of re-elevation arrived, or of that intermittent upward movement, when the ridges to be described in the next chapter were formed in succession, and, when valleys, like that of St. David's, which had been filled up, were partially re-excavated.

* J. L. Hayes, Boston Journ. Nat. Hist., 1844.

CHAPTER XX.

Mirage on Lake Ontario.-Toronto.-Excursion with Mr. Roy to examine the Parallel Ridges between Lakes Ontario and Simcoe.-Correspondence of Level in their Base-lines over wide Areas.-Origin of the Ridges.-Lacustrine Theory.Hypothesis of Sand-banks formed under Water.-Rapid Progress of the Colony.-British Settlers unable to speak English.

June 14, 1842.-FROM Queenstown we embarked in a fine steamer for Toronto, and had scarcely left the mouth of the river, and entered Lake Ontario, when we were surprised at seeing Toronto in the horizon, and the low wooded plain on which the town is built. By the effect of refraction, or "mirage," so common on this lake, the houses and trees were drawn up and lengthened vertically, so that I should have guessed them to be from 200 to 400 feet high, while the gently rising ground behind the town had the appearance of distant mountains. In the ordinary state of the atmosphere none of this land, much less the city, would be visible at this distance, even in the clearest weather.

Toronto contains already a population of 18,000 souls. The plain on which it stands has a gentle, and to the eye imperceptible, slope upwards from the lake, and is still covered, for the most part, with a dense forest, which is beginning to give way before the axe of the new settler. I found Mr. Roy, the civil engineer, expecting me, and started with him

86

RIDGES NEAR TORONTO.

СНАР. ХХ.

the morning after my arrival, to examine those ridges
of sand and gravel, and those successive terraces, at
various heights above the level of Lake Ontario, of
which he had given an account in 1837 to the Geo-
logical Society of London. No small curiosity was
excited, when his paper was read, by his endeavour
to explain the phenomena, by supposing the former
existence of a vast inland sea of fresh water, the
barriers of which were broken down one after another
until the present chain of lakes alone remained.

We started at an early hour from Toronto on
horseback, taking a direction due northwards through
the forest, and after riding for a mile over what
seemed a perfectly level plain, came to the first
ridge, the base of which my companion informed me
was 108 feet above Lake Ontario. This ridge rose
abruptly with a steep slope towards the lake, and
was from 20 to 30 feet high. Its base consisted of
clay, and its sandy summit, covered with pines, might
easily be traced eastward and westward by the dis-
tinctness of the narrow belt of fir-wood, on each side
of which other kinds of timber flourished luxuriantly
on the clayey soils.

Continuing our ride over the plain we arrived at the second ridge, a mile and a half farther inland, having its base 208 feet above the lake; this level, and the others afterwards to be mentioned, having been accurately ascertained by Mr. Roy when employed professionally in making measurements for several projected canals and railroads. The second ridge is a far more striking object than the first, being from 50 to 70 feet high above the flat and even ground on both sides of it. At its foot were a great

L

number of boulders of rocks which, by their composition, can be proved to have come from the north; and some few of which were perched on the summit of the ridge. Such transported fragments are rare on the soil between the ridges. Another ride of two miles and a half, in a northerly direction, brought us to the third ridge, five miles distant from the lakeshore, which was much less conspicuous than the preceding ones; it was indeed, at the point where we crossed it, little more than a steep slope of ten feet, by which we mounted to a higher terrace. The surface of this terrace was only 80 feet above the base of the second ridge, so that the top of the latter, in those places where it is 70 feet or more in height, is nearly on a level with the bottom of the third ridge, or cliff.

In this manner we went on, passing one ridge or cliff after another, sometimes deviating from our course for several miles east and west, that my guide might point out to me the continuity of the ridges, and the uniformity of the level of their base-lines. This uniformity, however, though I have no doubt of its reality, I had no time to test by actual measurement. On tracing the same ridge for several miles east and west, I occasionally found it to vary greatly in height above the plain, and sometimes to divide into two. One of these sometimes formed a step immediately above the other, and sometimes diverged or branched off so as to form an upper and parallel ridge at some distance. They were all broken occasionally by deep narrow gaps, as I had observed in the Osars of Sweden.

I saw, on the whole, no less than eleven of these ridges, some of which might be called cliffs, or the

88

ORIGIN OF THE RIDGES

СНАР. ХХ

abrupt terminations of terraces of clay, which cover everywhere the subjacent Silurian rocks to a great depth, and belong to the drift or boulder formation. The highest ridge is about 680 feet above Lake Ontario, the water-shed between that lake and Lake Simcoe being 762 feet high. There is then a descent of 282 feet from that summit level to the shores of Lake Simcoe, which is 42 miles from Lake Ontario. On this northern slope of 282 feet, Mr. Roy has traced several of the higher ridges, at levels precisely corresponding to those which I saw on the southern side. He also assures me that several of the ridges, which exceed in height the level of the table-land between Lakes Ontario and Erie, extend continuously to the northern shore of Lake Erie; and in another direction agree with ridges on the uplands bounding the valley of the Ottawa river.

The identification, however, of horizontal planes at points several hundred miles distant from each other, requires a nicety and exactness of trigonometrical measurement, which cannot as yet have been bestowed on this region; and when there are so many terraces at levels differing but slightly from each other, and some of them occasionally dividing into two, an upper and a lower shelf, they may easily be confounded at remote points.

I shall content myself with stating that, with the exception of the parallel roads or shelves in Glen Roy, and some neighbouring glens of the Western Highlands in Scotland, I never saw so remarkable an example of banks, terraces, and accumulation of stratified gravel, sand, and clay, maintaining, over wide