The furthest sources of the Ottawa River are unknown.[143] It rises to importance at the outlet from Lake Temiscaming, 350 miles west of its junction with the St. Lawrence.[144] Beyond the Falls and Portage des Allumettes, 110 miles above Hull, this stream has been little explored. There it is divided into two channels by a large island fifteen miles long: the southernmost of these expands into the width of four or five miles, and communicates by a branch of the river with the Mud and Musk Rat Lakes. Twelve miles further south the river again forms two branches, including an extensive and beautiful island twenty miles in length; numerous rapids and cascades diversify this wild but lovely scene; thence to the foot of the Chenaux, wooded islands in picturesque variety deck the bosom of the stream, and the bright blue waters here wind their way for three miles through a channel of pure white marble. Nature has bestowed abundant fertility as well as beauty upon this favored district. The Gatineau River joins the Ottawa near Hull, after a course of great length. This stream is navigated by canoes for more than 300 miles, traversing an immense valley of rich soil and picturesque scenery. At the foot of the Chenaux the magnificent Lake des Chats opens to view, in length about fifteen miles; the shores are strangely indented, and numbers of wooded islands stud the surface of the clear waters. At the foot of the lake there are falls and rapids;[145] thence to Lake Chaudiere, a distance of six miles, the channel narrows, but expands again to form that beautiful and extensive basin. Rapids again succeed, and continue to the Chaudiere Falls. The boiling pool into which these waters descend is of great depth: the sounding-line does not reach the bottom at the length of 300 feet. It is supposed that the main body of the river flows by a subterraneous passage, and rises again half a mile lower down. Below the Chaudiere Falls the navigation is uninterrupted to Grenville, sixty miles distant. The current is scarcely perceptible; the banks are low, and generally over-flowed in the spring; but the varying breadth of the river, the numerous islands, the magnificent forests, and the crystal purity of the waters, lend a charm to the somewhat monotonous beauty of the scene. At Grenville commences the Long Sault, a swift and dangerous rapid, which continues with intervals till it falls into the still Lake of the Two Mountains. Below the heights from whence this sheet of water derives its name, the well-known Rapids of St. Anne's discharge the main stream into the waters of the St. Lawrence.[146]