226 FIRST YEAR COURSE IN GENERAL SCIENCE 



Young and growing mountains are likely to be the centers 

 of earthquake disturbance. By means of delicate instru- 

 ments for detecting and recording the direction of the 

 movement, scientists can locate the region where the rocks 

 parted, sometimes several miles below the surface. 



During volcanic eruptions, earthquakes are caused by the 

 sudden pressure of expanding steam, which has the effect 

 of a blow upon the rocks. When the steam finds an outlet, 

 the shaking ceases. 



246. Effects of Earthquakes. The vibrations of a 

 severe shock are felt in every direction for long distances 

 from the center of disturbance. But earthquakes make very 

 little change in the surface of the earth. They may cause 

 a landslide, or a lifting up of a piece of ground, or an 

 opening like a ditch varying from a few inches to some 

 feet in width; otherwise they make little change except 

 in man's handiwork. It is the suddenness of the shock 

 which damages buildings and thus causes loss of life. 



247. Famous Earthquakes. In " The One Hoss Shay," 

 Oliver Wendell Holmes refers to a disaster in Portugal in 

 1755: 



" That was the year when old Lisbon town 

 Saw the earth open and gulp her down. 



It was on that terrible earthquake day 



That the Deacon finished the One Hoss Shay." 



In 1812 a great depression of the surface occurred in Mis- 

 souri, and the most violent earthquake known to the United 

 States resulted. About seventy-five years later there was 

 an earthquake which was most severe near Charleston, 

 South Carolina. In one minute many houses were entirely 

 wrecked and thousands of chimneys were thrown down. 

 Outside the city, a rent some rods in length was made in 

 the ground. The shaking was felt, in a less degree, from 

 Boston to Cuba. These are the only serious earthquakes 



