364

HISTORY OF ENGINEERING.

Book I.

say, by dropping a large quantity of rough stones in a proper direction and width, so asto form an artificial rock or base for the pier ; these stones, sinking by degrees into the sand,

SECTION or l’ILK.

Fig. 365.

ST. IVES HARBOU

and being followed by others, will rest upon the former, and so on, till the lowest becomefirm; for the sand, lying very close and compact, will bear any weight when not affectedby the action of the sea. By this method more stone is required than if the pier be builtupon a regular base ; but the whole being of very rough stone, and executed withouttimber work, it will be cheaper and more secure than any thing can be made upon a foun-dation of piles and timber upon sand.

The pier, so raised to half tide, or even to the top, was to act as a breakwater or defenceagainst the sea, and Smeaton estimated that the cost would be 7s. 6d. per cube yard

The highest spring-tides being 26 feet above the surface of the sand, the pier was to becarried up solid to the height of 30 feet; and supposing the settlement in the sand to be6 feet, the whole height would be 36 feet. The pier was to batter half its height oneach side, and as the top was to be 24 feet in breadth, the base would be 60 feet, and themean breadth 42 feet; this multiplied by 36 feet, the height, gave a sectional area of168 yards.

Smeaton recommended that the shores should be planted with sea rushes, which werefound to entangle the sand, prevent its blowing about, and retain it in the north bay, whereit arises, and by this means the breadth of the neck of land that joins the island would beincreased.

Penzance harbour has a mole to protect it, but the port is dry at Ioav water.

Falmouth has a spacious port and quay, from whence the packets bound to Spain, Por-tugal, and the West Indies , take their departure.

Fowey is a small port at the mouth of a river of that name, and the town is built uponits w r estem bank.

Plymouth Sound , on entering, has to the east the celebrated breakwater; after passingwhich a natural basin is arrived at, into which the Tamar and Plym discharge themselves,forming the harbour, comprehending the three divisions of the Hamoaze, the Catwatcr, andthe Sound .