ngth and 100 in breadth, with a
circumference, including Green Bay, of 1300 miles. It contains 22,000
miles of surface, with a depth of 900 feet in the deeper parts, though
near the shore it grows gradually shoal. The rocks which compose its rim
are of a sedimentary nature, and afford few indentations for harbors.
The shores are low, and lined in many places with immense sand-banks.
Green Bay, or Bale des Puans of the Jesuits, on the west coast, is 100
miles long and 20 broad. Great and Little Traverse Bays occur on the
eastern coast, and Great and Little Bays des Noquets on the northern.
One cluster of islands is found at the outlet of the main lake, and
another at that of Green Bay. Lake Michigan is the only one of the Great
Lakes which lies wholly within American jurisdiction.

Lake Erie is 240 miles in length, 60 in breadth, and contains an area
of 9,600 square miles. It lies 565 feet above the sea-level, and is
the shallowest of all the Lakes, being only 84 feet in mean depth. Its
waters, in consequence, have the green color of the sea in shallow bays
and harbors. It is connected with Lake Huron by the St. Clair River and
Lake, a shallow expanse of water, twenty miles wide, and by Detroit
River.

Lake Ontario is 180 miles in length and 55 in breadth, containing 6,300
square miles. It is connected with Lake Erie by the Niagara River, and
also by the Welland Canal, which admits the passage of vessels of large
burden. This lake lies at a lower level than the others, being only 230
feet above the sea. It is, however, about 500 feet in depth.

The whole area of these lakes is over 90,000 miles, and the area of land
drained by them, 335,515 miles.

The presence of this great body of water modifies the range of the
thermometer, lessening the intensity of the cold in winter and of the
heat in summer, and gives a temperature more uniform on the Lake coasts
than is found in a corresponding latitude on the Mississippi.

The difference between the temperature of the air and that of the
Lakes gives rise to a variety of optical illusions, known as _mirage._
Mountains are seen with inverted cones; headlands project from the shore
where none exist; islands clothed with verdure, or girt with cliffs,
rise up from the bosom of the lake, remain awhile, and disappear.
Hardly a day passes, during the summer, without a more or less striking
exhibition of this kind. The same phenomena of rapidly varying
refraction may often be witnes