At the corner of Nassau street, and looking down into Broad street, is the Sub-Treasury of the United States, a handsome white marble edifice. It is built in the Doric style of architecture, and its massive flight of steps and imposing portico give to it a striking appearance. It is constructed in the most substantial manner, and has a rear entrance on Pine street. The interior is handsomely arranged, and tasteful but secure iron gratings protect the employees from surprise and robbery. The vaults are burglar proof. This is the principal depository of the Federal Government, and millions of dollars are always in its vaults. The building was erected for, and was used for some years as, a Custom House. From the steps of the Treasury one may enjoy a fine view of the entire street, and of Broad street also. About the hour of noon the scene is busy and exciting. The roadway in Wall street is full of struggling vehicles, and long rows of cabs stand in waiting in Broad street for the busy operators within the Exchanges. The side walks are crowded with an eager, hurrying throng. The steps and street around the Stock Exchange, in Broad street, are black with men who are shouting, pushing, and struggling in the effort to turn the transactions of the day to their advantage. Overhead is an intricate maze of telegraph wires, along which flow the quick and feverish pulsations of the great financial heart of the country. The sunlight falls brightly and cheerily over it all, and at intervals the clear, sweet chimes of old Trinity come floating down the street high above the noise and strife below them. Diagonally opposite the Treasury, and at the corner of William street, is the Custom House, which occupies the irregular square bounded by Wall street, Exchange Place, William street, and Hanover street. It is one of the finest and best arranged edifices in the city. Just below the Custom House is the handsome marble building of Brown Brothers, one of the model houses of New York, as regards both the firm and the edifice. The Messrs. Brown are regarded as the most reliable and accomplished operators in the street. Across the way, in a dingy granite building, is the office of August Belmont & Co., the American agents of the Rothschilds, and bankers on their own account. Jay Cooke & Co. occupy the fine marble building at the corner of Wall and Nassau streets, opposite the Treasury, and there conduct the New York branch of their enormous business. Fisk & Hatch, the financial agents of the great Pacific Railway, are a few steps higher up Nassau street. Henry Clews & Co. are in the building occupied by the United States Assay Office. Other firms, of more or less eminence, fill the street. Some have fine, showy offices, others operate in dark, dingy holes. II. THE STOCK EXCHANGE.