288 



PHYSICAL GEOLOGY 



In Arizona the waters of several streams now flow into a fissure 

 formed during an earthquake (Fig. 286). In some earthquakes 



fissures have opened 

 and then closed 

 again, entrapping 

 people and animals, 

 and engulfing houses. 

 Changes in Level. 

 — It is usual to find 

 that the level of the 

 land has changed 

 during earthquakes. 

 As a result of the 

 earthquake of 181 1- 

 181 2 in the Missis- 

 sippi Valley, Reelfoot 

 Lake, 25 miles long 

 and 5 miles wide, was 

 formed, the trees still 

 being visible on its 

 bottom. In the same 

 earthquake Lake 

 Eulalie was drained. 

 In the Indian earth- 

 quake of 1819, a lake 

 about the same size 

 as Reelfoot Lake was 

 formed. There is 

 also often a lateral 

 shifting of the ground 

 during an earth- 

 quake, as in that at San Francisco, which moves the plains or 

 mountains in one direction on one side and those on the opposite side 

 in the opposite direction (p. 278). The changes of level on opposite 

 sides of faults which produce falls and lakes have already been dis- 

 cussed (p. 262) (Fig. 287) ; elevation is as frequent an accompaniment 

 of earthquakes as depression. During the earthquake which shook 

 lower India in 18 19, an area 50 miles long and 10 miles broad was 

 elevated 10 feet and is called the Mount of God. Over an area of 

 600,000 square miles the coast line of Chile and Patagonia is said to 



Fig. 286. — Fissure produced at the time of an 

 earthquake. Arizona. (U. S. Geol. Surv.) 



