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earthquake movement which visited Syria in 1837, was felt in a line five hundred miles long, by ninety miles wide.
In accordance with a general law in mechanics, the undulations of horizontal earthquake movements finish by cracking the superficial soil and strata of the earth's crust. In the earthquake which, in 1811, convulsed the district of New Madrid, South Carolina, the surface earth between New Madrid and Little Prairie rose in great undulations to a considerable height, till the earth waves burst, when volumes of water and sand, and masses of pit-coal, were hurled up through the crevices high into the air; large lakes of twenty miles in extent were on this occasion formed in the course of a single hour, whilst some of the ancient lakes of the district were drained and completely dried up. As a general rule, horizontal shocks proceeding onward unresisted, are not considered to be very dangerous. The most terrible horizontal earthquakes are those where the shocks, proceeding from two different foci of action, happen to cross each other. A town standing on the ground at the point of intersection of the two waves has little chance indeed of escaping the crash and crush produced by their meeting.
In the circular or gyratory movement, the earthquake action moves in a circuit, sometimes very extensive, in other, but rare instances, of very small compass; in the latter case, the movement proves