polished. The whole surface of New York Island, where the rock is exposed, shows marks of glacial action, the upturned edges of gneiss being ground off to form a nearly plane surface, or, where ridges of more massive rock had existed, these are rounded over to form roches moutonnées. Fine examples of the latter may be seen in Central Park and on the east side of the island near Harlem.

The material which occupies so much of the troughs of the Hudson and East River is mostly glacial drift, clay, gravel, sand, and bowlders, scraped from the highlands by the great ice-sheet into these preglacial gorges. It is probable they were once filled to the brim, and that they were subsequently reëxcavated in part by the floods of water which resulted from the melting ice. After these ceased, and they were occupied by water standing at its present level, and moved only by tidal action, they were more or less silted up by the deposit of fine mud brought down by the larger and smaller streams, here checked in their

The southern and lower

flow and losing their transporting power. portion of New York Island, which was under the lee of the higher, was covered with deposits left by the retreating glacier, and these were never afterward entirely removed. Here are now beds of sand and gravel which have in places been penetrated to the depth of one hundred feet or more. On the higher parts of the island and the adjacent country, the rock is generally bare or covered with soil, but even here depressions are filled with bowlders, clay, or gravel, often to the depth of several feet, and large transported bowlders are everywhere scattered over the surface. These latter have sometimes been derived from the rocks of the island, but most of them seem to have come from distant points, and always from the north and west. Rounded masses of trap are very common among the bowlders, and these have been brought across the Hudson, for there is no trap in place on the east side of the river. The trap-ledge which forms the summit of the Palisades is everywhere worn and scratched by glacial action, and the markings which it bears are generally concordant in direction with those of the rocks of New York Island and Westchester County, viz., about northnorthwest and south-southeast. Even on the river-face of the hills which form the east bank of the Hudson, the bearing of the glacial scratches is essentially the same, showing that the movement of the great ice-sheet was little affected by any such trifling irregularity of the surface beneath it as the Hudson Valley.

We have no measure of the amount of erosion which New York Island and the adjacent country suffered during the Ice period, but it is not improbable that a mass a hundred feet in thickness was taken from the surface of all the region occupied by the ice.

Most of the finer material ground up by the glaciers was washed out to sea and deposited as the "Champlain clays." Of these there is very little showing in the vicinity of New York, since none of the coast from this point southward has been raised to display them; but a great continental elevation has since taken place toward the north, bringing them at Croton Point 100 feet, at Albany 250, at Burlington 400, at Montreal 500, at Labrador 800, at Davis Straits 1,000, and at Polaris Bay 1,800 feet above the present sea-level.

The coarser portion of the grist ground by the glacier remains as beds of gravel and sand, or heaps of bowlders scattered over the surface of the country where they were left as local moraines, or as the gravelbars of streams flowing beneath the glacier. The greatest accumulation of material transported by the ice in all the country about New York is seen on Long Island, which is indeed a great terminal moraine heaped up along the margin of the continental glacier. As is generally known, Long Island is mostly composed of heaps of gravel and sand, which sometimes form hills from 200 to 300 feet in height, and in these no solid rock has been found in any exploration yet made. The formation of this huge gravel-bank seems to have been, in brief, as follows: The great ice-sheet, moving down from the north in Connecticut and Southern New York, passed over a region occupied mostly by hard, crystalline rocks. These were extensively worn away by it, and much of the material taken from the surface was pushed on as by a great scraper to its margin. When the ice-sheet reached the line of Long Island Sound, it passed from the area of upturned crystalline rocks on to the comparatively soft horizontal Tertiary and Cretaceous strata, which here formed a plain stretching seaward, from the highlands, just as they now do in New Jersey and more southern States. These were scooped out to form the basin of Long Island Sound, and the material excavated from it, as well as much brought from the country lying farther north, was banked up between this basin and the ocean. Thus it will be seen that, of the water-connections of New York Harbor, Long Island Sound is much the most modern; and yet, as a part of it occupies the site of the valley of a large stream-the Housatonic, with perhaps the Connecticut-which passed through the Hell Gate gorge, its formation must have been begun in preglacial times.

As has been said, the rock foundations of Long Island are almost entirely concealed, but a number of cases are reported of the penetration in wells of strata containing Cretaceous fossils, and there is little doubt that the Cretaceous series of New Jersey and Staten Island, represented by the Raritan sands, and the Amboy, Keyport, and Staten Island clays, once formed a continuous margin to the continent, all the way around

to Nantucket. These strata still probably underlie a large part of Long Island where they have been protected from erosion by the heavy beds of drift that cover them, while the shore-waves have eaten away all exposed portions. Evidence strongly confirmatory of the view that Cretaceous rocks have been scooped out of the basin of Long Island Sound is afforded by the fact that the drift of Long Island contains in immense numbers imperfectly-rounded blocks of a reddish-brown sandstone, filled with the impressions of dicotyledonous leaves-a rock nowhere yet found in place, but one which is probably the representative of the leaf-bearing Cretaceous sandstone of the Raritan River.

Whether the overlying Tertiary beds will be found on Long Island is perhaps doubtful, since they are not conterminous with the Cretaceous; but, from the fact that an outlier of this formation exists at Gay Head, Martha's Vineyard, it is highly probable that it was once continuous from Southern New Jersey.

On the preceding pages the history of the vicinity of New York has been traced backward for some millions of years. This history has been read from rock-graven records, which, although meagre and mutilated, give the generalities of the narrative with a truth and fidelity which shame all human history. It would be a pleasant duty to predict the future of this region, even in the same degree of fullness; but the future is as unknown to the geologist as to others. He learns, however, from his studies, that what we call terra firma is a type of instability, and that there is nothing stable but the law of change; and he can prophesy with confidence that in the distant future the history of the distant past will be, in part at least, repeated. Even now changes are in progress which, if they should continue a few thousand years, would very profoundly affect not only the aspects of this region, but its adaptability to human occupation. A number of facts indicate that the coast of New Jersey and Long Island is gradually sinking. From the marshes of New Jersey are taken the trunks of trees which could not have grown there except when it was drier ground, and on the shore stumps are seen, now under water, of trees which must have grown on land. So, too, the sea throws up in storms portions of turfy soil, once covered only by the air, and similar soil has been reached below the sea-level in pits dug through drifted sand along its margin. It is also said that the land boundaries have been changed and farms diminished even where the wash of the shore-waves produced no effect. The rate of this subsidence is very slow-only a few inches in a century—and it may at any time be arrested or reversed; but, should it continue, as it may, for some thousands of years, it would result in a submergence of land now valued at hundreds of millions of dollars, and a complete change of position in the seats of commerce and industry, which must always centre about this harbor. This possible catastrophe is, however, so uncertain and remote that it seems hardly sufficient to disturb the equanimity of at least this generation of inhabitants.

III. WHY NEW YORK IS THE COMMERCIAL METROPOLIS OF THE UNITED STATES.-The great commercial advantages of the site of the city of New York attracted the attention of the first voyagers who came to these shores. When Hendrick Hudson, passing through the Narrows, found within a commodious, landlocked harbor, and a broad and beautiful river, which floated his ships in safety more than a hundred miles into the interior of the continent, he clearly foresaw, and predicted, that this would be the great entrepot of foreign trade for the New World. The subsequent history of New York has fully demonstrated the advantages of its position, since a population of more than 2,000,000 has gathered immediately around its harbor, and it has become not only the business metropolis of a great nation, but the second in importance of the markets of the world. Those who have witnessed and shared the progress and prosperity of the city have been generally well satisfied to enjoy these, without any special inquiry into the causes which have produced them; and, indeed, it is not unlikely that they have accepted them as simply the fruit of their own intelligence and energy. It is doubtful, however, whether the merchants of New York have been more shrewd and enterprising than those of the other ports on our coast. It is not flattering to the vanity of men to assert that they are what their surroundings make them, but it is nevertheless in a great measure true, and New-Yorkers are probably no exception to the rule. The real secret of the unparalleled growth of New York lies in the peculiar topography of its vicinity.

The city is set on an island, of which the shore on every side is swept by tide-water. On the west it is bounded by the Hudson—river we call it, but really an arm of the sea-in which the ebb and flow of the tide are perceptible as far as Troy, one hundred and fifty miles from its mouth. On the east the island is encircled by tideways called Spuyten Duyvel Creek, Harlem River, and East River, the latter a deep channel which connects New York Harbor with Long Island Sound, and thus affords an important artery of internal commerce, and another outlet to the ocean. These two great natural canals, the Hudson and East Rivers, embracing the long and narrow island between them, unite in New York Harbor, one of the most beautiful and commodious in the world. Seen from the city, it seems to be completely landlocked, but communicates with the ocean through the Narrows, with Newark Bay through the Kill van Kull, and thence by Arthur's Kill with Raritan Bay.

Thus it will be seen that New York Harbor is the centre of a series of navigable tideways which add greatly to its adaptation to the wants of commerce, and constitute the most peculiar physical features in its surroundings. The little map given on the next page will show the connection of this system of water-ways more distinctly than any verbal description can.

To those who have not made topography a study, the interest and mystery of the origin of the navigable channels leading into New York

Harbor will not be apparent, and it may seem an easy explanation to assume that they have been formed by the ebb and flow of the tide which sweeps through them. The tides at New York, however, do not rise to a great height, and have very little eroding power. It should also be said that the channels are far too deep to have been cut by any agents now in operation. For instance, at Polhemus's Dock the depth of Hell

Gate channel is 170 feet, and there are many places in the East River where the depth is over 100 feet. The greatest depth of water in New York Harbor and the Hudson River is about sixty feet, but this does not represent the true depth of the channels, since they have been very much silted up, and their rock-bottoms are probably 200 or 300 feet below the water-surface. If they could be cleared of clay, sand, and gravel, they would be seen to be narrow gorges cut in solid rock as deep as that of Niagara, and resembling some of the cañons of the Western rivers. It is therefore certain that they could not have been produced by tidal action. There are only two ways in which such chasms could be formed: first, by earthquakes, opening fissures in the rocks; and, second, by the erosion of flowing streams. That they are not earthquake fractures is certain, since no such fissures are found in the country about in the line of these channels, and their rocky walls show no sign of disturbance, being similar on opposite sides, and doubtless continuous below. They have, in fact, been formed by draining streams when this part of the continent stood much higher than now above the ocean-level. The evidence of this is cumulative and conclusive. The facts which prove it are, briefly, as follows:

1. The trough of the Hudson has been shown, by the soundings of