194 LIGHT SCIENCE FOR LEISURE HOURS. 



districts of active with those of extinct volcanoes. It 

 is said that in Chili a year scarcely ever passes with- 

 out shocks of earthquake being felt ; in certain re- 

 gions, not even a month. A similar persistence of 

 earthquake disturbance characterises Peru. Yet, al- 

 though both districts are shaken in this manner, there 

 seems to be a distinct evidence of alternating disturb- 

 ance as respects the occurrence of great earthquakes. 

 Thus in 1797 took place the terrible earthquake of 

 Riobamba. Then, thirty years later, a series of great 

 earthquakes shook Chili, permanently elevating the 

 whole line of coast to the height of several feet. Now, 

 again, after another interval of about thirty years, the 

 Andes are disturbed by a great earthquake, and this 

 time it is the Peruvian Andes which experience the 

 shock. Between Chili and Peru there is a space 

 upwards of five hundred miles long, in which no vol- 

 canic action has been observed. Singularly enough, 

 this very portion of the Andes, to which one would 

 imagine the Peruvians and Chilians would fly as to a 

 region of safety, is the part most thinly inhabited, in- 

 somuch that, as Von Buch observes, it is in some 

 places entirely deserted. 



Near Quito the trembling of the earth is almost in- 

 cessant, according to M. Boussingault. He considers 

 that the frequency of the movement is due rather to 

 the continual falling in of masses of rock which have 

 been fractured in recent earthquakes, than to the per- 

 sistence of subterranean action. He adds that the 

 height of several mountains in the Andes has diminished 

 in modern times. He refers, doubtless, to the Peruvian 



