The Elements of economic geology

Bibliographic data

Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part IV. Engineering geology

Collection:: Economics Books

242 ECONOMIC GEOLOGY from 50-100 fathoms, the sea-bed begins its long descent to the oceanic floors. This shelf has been regarded as either a great plain of marine erosion, or a submerged peneplane ; but it is too wide and deep to have been cut by the tide, and is more regular and extensive than any peneplane. The explanation has been given by Nansen, who attributes the shelf to waves spreading loose material evenly over the sea-floor, filling up depressions, and wearing down rock ridges. RATE oF MARINE ABrAsioNn—The rate of marine abrasion varies with the strength of the rocks and their exposure. The loss of land on the southern coast of Yorkshire is estimated at 3 yards per annum for the past century, and a total of 3} miles since Roman times. A British Association Committee on Coast Erosion reported in 1895 that the York- shire coast during the 37 years, 1852-89, had lost 5 feet 10 inches per annum. The recession is also rapid at exposed positions in Norfolk and Kent. The question whether this process is a national danger was investigated by a Royal Commission on Coast Erosion (1906-11); the evidence proved that the British Isles gain from the sea more than they lose. In the 35 years, 1848-93, 774 acres were lost on the Yorkshire coast, but 2171 acres were reclaimed within the Humber. The cliffs in Southern-eastern Yorkshire are so high that for every square yard lost 3 square yards are gained by the redeposition of the material elsewhere; as the new land is Crown property the gain is national. The total loss to the United Kingdom between 1848 and 1893 was 6640 acres; but over 49,000 acres were gained. Subaerial erosion, though less spectacular than marine abrasion, has greater effects. Subaerial lowering of the land has been estimated at about 1 foot in every 10,000 years ; the British coasts undergoing abrasion probably do not lose on an average more than 5 feet a century. The average height of England is about 650 feet. Hence the whole land would be reduced to sea-level by subaerial denudation in 6% million years, during which marine abrasion would have removed a strip 65 miles wide, from part only of the coast. Coastar Accrerion—The land may be extended seaward by the formation of beaches, bars, and deltas, and the filling of bays and estuaries. The first stage in the filling of a bay

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