The Island of Michilimackinac, in the strait connecting Lake Huron and Lake Michigan, is important in a political point of view, being the Gibraltar of the north-west. It is of an elliptical form, about seven miles in circumference, rising gradually to the centre;its figure suggested to the mind of the Indians its appropriate name, Michi Mackina,[27] (Great Turtle.) The greater part of the island is almost an impenetrable thicket of underwood and small trees, which contribute materially to the defence of the garrison. Fort Holmes stands on a summit of the island, several hundred feet above the level of Lake Huron, and is now one of the most formidable positions in the western country. The French were the first settlers, and their descendants, to a considerable number, reside near the Fort.
Maniton Island is situated near the eastern coast of Lake Michigan; it is six miles long and four wide, and is held sacred by the Indians. The Castor Islands are a chain of islets, extending from Grand Traverse Bay nearly across the lake; they are low and sandy, but afford a shelter for light boats in their passage to Green Bay. Grosse Isle is a valuable alluvion of several thousand acres, being five miles long, and from one to two wide.
GENERAL REMARKS ON ISLANDS.
It has been well observed, that a large island is a continent in miniature, with its chains of mountains, its lakes, rivers, and not unfrequently its surrounding islets. The smaller islands are found single, or in groups. Among the low or flat islands, there are some which are only banks of sand, scarcely raised above the surface of the water; sometimes they consist of masses of shells or petrifactions, as the Isles of Lachof to the north of Siberia, which are nothing but masses of ice, sand, and the bones of the mammoth. The Pacific contains a great many islands formed of coral reefs, which are sometimes covered with sand, and afford nourishment to a few plants.
Among the more elevated islands we find very many which owe their foundation, in a great measure, to volcanic agencies. Submarine islands, as they have been sometimes called, or immense sand-banks, covered with shoal water, are not unfrequent. Chains of islands in the neighborhood of continents seem to be often formed by the action of the waters washing away the less solid parts, which once occupied the spaces between the mountains and rocks. In this manner were probably formed the islands along the coast of the United States, which still appear above the surface of the waves.
One of the chief advantages that islands derive from their situation is, that the climate is generally rendered mild and salubrious, from the vapors of the surrounding sea, which generally moderate the violence of heat and cold, both of which are sensibly less than on the continent in the same latitude. Another advantage is found in their accessibility on every side, by which islands are open to receive and export commodities, and at times when the ports of the continent are closed. An island has on all sides the most extensive and effectual frontier, subsisting forever without repairs and without expense; and, which is still more, derives from this very frontier, a great part of the subsistence of its inhabitants, and a valuable article in its commerce, from fisheries.
The island of Acroteri, famous in ancient history, is represented to have risen from the sea, in a violent earthquake; its surface is composed of pumice-stone incrusted with a covering of fertile earth. Four neighboring islands have been attributed to a similar cause, and yet the sea about them cannot be fathomed by any sounding line. These have risen at different periods, the last in 1573, the first long before the birth of Christ. Similar eruptions of islands have occurred in the group of the Azores. Thus in December, 1720, a violent shock of an earthquake was felt at Tercera. During the night, the top of a new island appeared, which ejected a huge column of smoke. The pilot of a ship who attempted to approach it sounded on one side of the new formed island, but could not reach bottom with a line of sixty fathoms. On the opposite side, the sea was deeply tinged with various colors, white, blue and green, and was very shallow. This island gradually diminished in size, and finally altogether disappeared.
History abounds with accounts of floating islands, but they are either false or much exaggerated. These islands are generally found in lakes, and are composed of the light matter floating on the surface of the water in cakes, forming, with the roots of plants, collections of different sizes, which, not being fixed in any part to the shore, are driven about by the winds. In the course of time, some of them arrive at considerable size. The floating islands, however, mentioned by the old writers, have now disappeared or become fixed.