The vessels employed for carrying of the large blocks of stone, are of a peculiar construction, dapted to convey, with ease, masses of marble weighing from three to five tons each. These great blocks of marble are placed on trucks at the quar ries, and run down from thence, on iron railways, to the quays, against which the weasels lie with their sterns. The two stern ports are made sufficiently large to receive the trucks with the stones upon them. Each truck is passed separately through the port-hole, on an inclined plane, and run to the fore part of the vessel, in the hold, on an iron railway.
7 The two sides of the hold of the vessel are calculat ed each to contain eight of these loaded trucks, which, at five tons on each truck, gives 80 tons of stone for one cargo. The stones thus placed on the trucks remain till the vessel arrives at the point in the line of the Breakwater where they are to be de posited. By means of a crane on the deck of the vessel, the two trucks nearest to the two stern ports are then drawn up the inclined plane, and run upon a frame on movable binges, called the frame; by the falling of this frame, in the manner of a trap door, the stone or stones are discharged from the trucks on the slope of the Breakwater ; but the typ . ing-frame remains, by means of a catch, in the posi tion in which it is left at the moment of discharging the stones, until the empty truck is pulled up by the crane to the after-pert of the deck, from whence it is run forward to make room for the second pair of loaded trucks in the hold. The catch being now disengaged, the typing-frame returns to its former position, ready to receive the next pair of loaded trucks, and so on till the whole sixteen have been discharged, and the light trucks run upon the deck of the vessel, ready to be run out at the quay, and from thence to the quarries, to take in fresh loads of stone. In this manner a cargo of 80 tons may be
discharged in the space of 40 or 50 minutes. The vessels are placed in the proper places for deposit ing the same by means of buoys, and the exact line of the Breakwater is preserved, by observing lights or staves placed at a distance on the shore.
The following description, referring to Plate XXXIX., will convey an accurate idea of these excel lent vessels for the purpose they were constructed.
Fig. 1. Shows the stern of the vessel, in the act le depositing the stones. The runner R being booked to thefore.part of the truck, raises it up, and by that means tips the stone overboard. When the stone is in the act of being drawn up out of the hold, on the inclined plane B (fig. 3.), the miner is hooked to the fore-part of the truck, and lashed down to the •fter-end, over the stone, which prevents the latter from sliding off the truck, in its progress up the in. dined plane. The empty trucks are, for the most part, lodged on the forepart of the deck, and some placed on an edge against the aide of the vessel.
Fig. 2. Shows the stern of the vessel when laded, with the ports up, or closed.
Fig. 8. A longitudinal or sheer-section of the ves eel, when loaded, with the trucks on one side of the bold and deck, showing the number which the ves sel usually stows on each side. The stones being frequently longer than the trucks, the number car ried in the •hold must be proportioned accordingly. In bad weather it is unsafe to send many trucks on deck ; and, in general, not more than four are sent into the Sound, in that way, at one time ; the a mount of the cargoes, therefore, vary according to circumstances, from 40 to 65 tons ; the largest stone hitherto deposited being about eight tons.
The after-part of the deck, under the tiller, is di vided into two parts, length ways, and made to move op and down ; the fore-parts are secured to a beam