The great line of communication is established, 400 miles in length, between Philadelphia and Pittsburg, on the left bank of the Ohio, composed partly of railway and partly of canal. The section from Philadelphia to Columbia (82 miles) is railway; the line is then continued by canal for 172 miles to Holidaysburg; it is then carried by railway 37 miles to Johnstown, whence it is continued 104 miles further to Pittsburg by canal. The traffic on this mixed line of transport is conducted so as to avoid the expense and inconvenience of transhipment of goods and passengers at the successive points where the railway and canals unite. The merchandise is loaded and the passengers accommodated in the boats adapted to the canals at the dépôt in Market-street, Philadelphia. These boats, which are of considerable magnitude and length, are divided into segments by partitions made transversely and at right angles to their length, so that such boat can be, as it were, broken into three or more pieces. These several pieces are placed each on two railway trucks, which support it at the ends, a proper body being provided for the trucks adapted to the form of the bottom and keel of the boat. In this manner the boat is carried in pieces, with its load, along the railway. On arriving at the canal the pieces are united so as to form a continuous boat, which being launched, the transport is continued on the water. On arriving again at the railway the boat is once more resolved into its segments, which, as before, are transferred to the railway trucks and transported to the next canal station by locomotive engines. Between the dépôt in Market-street and the locomotive station which is situated in the suburbs of Philadelphia the segments of the boat are drawn by horses on railways conducted through the streets. At the locomotive station the trucks are formed into a continuous train and delivered over to the locomotive engine. As the body of the truck rests upon a pivot, under which it is supported by wheels, it is capable of revolving, and no difficulty is found in turning the shortest curves, and these enormous vehicles, with their contents of merchandise and passengers, are seen daily issuing from the gates of the dépôt in Market-street, and turning with facility the corners at the entrance of each successive street.