Most of them are barred at their mouth with sand. II. RIVERS WHICH FLOW INTO THE ATLANTIC. The _River St. Croix_ forms a part of the eastern boundary of Maine, and is little navigable except by rafts; most of it consists of a chain of small lakes. From Calais to the sea, thirty miles, its navigation is unobstructed. The _River Penobscot_ is the largest in the state of Maine. It rises in the highlands separating Maine from Lower Canada. Between the junction of its two upper branches is Moosehead lake, about forty miles long, and fifteen wide. From the _Forks_, as they are called, the Penobscot Indians pass to Canada, up either branch, principally the west, the source of which is said to be not more than twenty miles from the waters which fall into the St. Lawrence. The whole navigable course of the river for sloops, is forty-six miles from the head of the bay, to near the head of the side; and from the Forks to the sea is one hundred and thirty-four miles. This river has very numerous branches, navigable by rafts and abounding in mill sites. The _Saco_ rises in the White Mountains of New Hampshire, enters Maine at Fryeburg, and flows in an irregular course south-east to the sea; it is one hundred and sixty miles long, and has numerous falls which afford excellent mill sites and manufacturing stations. The _Androscoggin_ rises in Umbagog lake, among the highlands which form the north-west boundary of Maine, and descending through a succession of lakes enters New Hampshire at Errol; it re-enters Maine at Gilead, and flows east and south till it joins the Kennebec at Merrymeeting bay. Its length is one hundred and forty miles; the whole course is broken by rapids and falls, which prevent the transportation of any thing except timber and logs. The _Kennebec_ also rises in the highlands, near the sources of the Androscoggin, and flows nearly south to the sea; falls and rapids render the navigation difficult above the tide at Augusta, from which place it is navigable for vessels of one hundred tons, and from Hallowell and Gardiner for ships to the sea. The country watered by the Kennebec generally consists of excellent land; it is one of the best grazing districts in New England; and there are upon the banks of the river a number of flourishing and handsome towns.