The southern portion is densely built up. Between the City Hall and Twenty-third street New York is more thickly populated than any city in America. It is in this section that the "tenement houses," or buildings containing from five to twenty families, are to be found. The greatest mortality is in these over-crowded districts, which the severest police measures cannot keep clean and free from filth. The southern portion of the city is devoted almost exclusively to trade, comparatively few persons residing below the City Hall. Below Canal street the streets are narrow, crooked, and irregular. Above Houston street they are broad and straight, and are laid out at regular intervals. Above Houston street, the streets extending across the island are numbered. The avenues begin in the vicinity of Third street, and extend, or will extend to the northern limit of the island, running parallel with the Hudson River. There are twelve fine avenues at parallel distances apart of about 800 feet. Second and Eighth are the longest, and Fifth, Madison and Lexington the most fashionable. They commence with Avenue D, a short street, near the East River. West of this, and parallel with it, are three avenues somewhat longer, called Avenues C, B, and A, the last being the most westerly. Then begin the long avenues, which are numbered First, Second, and so on, as they increase to the westward. There are two other avenues shorter than those with numbers, viz: Lexington, lying between Third and Fourth, and extending from Fourteenth street on the south to Sixty-ninth street on the north; and Madison, between Fourth and Fifth, and extending from Twenty-third street at Madison Square to Eighty-sixth street. Madison and Lexington are each to be prolonged to the Harlem River. These avenues are all 100 feet wide, except Lexington and Madison, which are seventy-five feet wide, and Fourth avenue, above Thirty-fourth street, which is 140 feet wide. Third avenue is the main street on the east side above the Bowery, of which it is a continuation, and Eighth avenue is the principal highway on the west side. Fifth and Madison avenues are the most fashionable, and are magnificently built up with private residences below the Park. The cross streets connecting them are also handsomely built. The numerical streets are all sixty feet wide, except Fourteenth, Twenty-third, Thirty-fourth, Forty-second, and eleven others north of these, which are 100 feet wide. The streets of the city are well laid off, and are paved with an excellent quality of stone. The sidewalks generally consist of immense stone "flags." In the lower part of the city, in the poorer and business sections, the streets are dirty and always out of order. In the upper part they are clean, and are generally kept so by private contributions.