IIAND-BOOK OF WASHINGTON. 13 street cast, 1st street west. Thus duplicate streets run parallel with each other, but differ only by having north or south, and east or west attached. The avenues run diagonally across the streets. Three of these avenues intersect at the Capitol and three at the President’s House, and an addi tional one, Pennsylvania. This grand thorough fare is very fine, being spacious, regular, and beautiful, running the whole length of the city, from the Eastern Branch to the Itock Creek, em bracing in its long stretch the Capitol, Presi dent’s House, and numerous other objects of interest, which is a noble feature, worthy of the admiration so universally bestowed. THE PO TO II AO RIVER. Which passes along the District, is one of the broadest, and in several respects the most beau tiful in the United States. It has its rise in the Alleghany mountains. This river, after a mean dering course of about 400 miles, falls into the Chesapeake Bay, about 100 miles below its head.