EARTHQUAKES

are probably caused by a change in the weight of the earth’s crust, and this is caused mainly by the removal of ma es of soil from mountain tops to the ocean floor. Therefore, a low plain at a great distance from the ocean ought to be exempt from them. E. in Britain happen most often, though very slightly, at Comrie, where slight shocks are felt almost every year. Of the more distinct shocks, 31 started in Wales, and 31 along the south coast of England. The most serious that has occurred in Britain for four centuries started on the E ex coast on April 22, 1884, and did a great deal of harm in and round Col chester. The three worst E. on record in the world are the one of 1693 a.d. in Sicily, which destroyed 100,000 persons; that of 1703 A.D. at Yeddo, which destroyed 200,000; and that of 1731 A.D. at Pekin, which also destroyed 100,000.