PORTLAND, ISLE OF, properly a peninsula on the coast of Dorsetshire, England; Chesil Bank connects it with the main land. Pop. (1931), 12,018. It is 4m. long and nearly I 1- in ex treme breadth, with an area of about 44 sq.m. The shores are precipitous, and Portland is inaccessible from the sea except towards the south. The highest point is the Verne hill in the north. A raised beach is seen at Portland Bill. The substratum of the island is Kimmeridge clay, above which rest beds of sand and strata of Oolitic limestone, widely famed as a building stone. In the "dirt-bed" resting upon the Oolitic strata numerous specimens of petrified wood are found, some of great size. The soil, though shallow, is fertile, and the isle is famed for its mutton. Quarry ing, fishing and agriculture are the chief industries.
The G.W.R. and S.R. have a joint line south from Weymouth to Portland and Easton. On the isle are the famous prison build ings. Portland castle, built by Henry VIII in 1520, is generally occupied by the commander of the engineers or of the regiment stationed on the island. On a rock on the eastern side are re
mains of a more ancient fortress, Bow and Arrow castle, ascribed to William Rufus.
A harbour of refuge was built by the Admiralty 1847-62. A breakwater stretching northwards from the north-east corner of the island partially enclosed a large area of water naturally shel tered on the south and west. An inner arm ran nearly east from the island to a masonry head and fort, and an outer detached arm bent north to a circular fort, a narrow entrance for shipping be ing left between the two. Two new breakwaters were built after 1895 to close the gap between the end of the outer breakwater and the Bincleaves rocks near Weymouth. These structures all consist of rubble mounds. The defensive harbour thus completely enclosed has an area of 2,200 acres to the one-fathom line, of which 1,500 acres have a depth of not less than 3o ft. at low water.