238 HOVEY— EARTHQUAKES : [April 2±, 



northern and southern Andes. This " Circum-Pacific " or " Andes- 

 Japan-Malay " belt has given 41 per cent, of the quakes. In the 

 western hemisphere in addition to a part of the circum-Pacific belt, 

 there are the West India Islands and the mountains of Venezuela 

 forming a seismic zone. Earthquakes mostly of volcanic origin have 

 visited many of the islands of the South Seas. The major portions 

 of Africa and South America remain blank upon such a map, 

 probably because little is known about their seismicity. 



We are in the habit of thinking of eastern North America as a 

 region free from earthquake shocks. The impression, however, is 

 erroneous, since New England has experienced about 250 recorded 

 shocks since the Pilgrims landed at Plymouth, and there have been 

 at least four great earthquakes in the eastern half of the continent 

 within the past two and one half centuries, one on the fifth of Feb- 

 ruary, 1663, which affected the St. Lawrence Valley over an area 

 more than six hundred miles long and three hundred miles wide as 

 described in the "Jesuit Relations."^ In 1811-1812 heavy quakes 

 occurred in the central part of the Mississippi Valley, accompanied 

 with considerable subsidence fifty miles south of the junction of the 

 Ohio and Mississippi Rivers. Strong shocks continued for more 

 than a year and evidence of the sinking still persists in lakes and 

 submerged trees. The southeastern part of the United States was 

 the center of an earthquake shock January 4, 1843, the waves of 

 which were felt at points at least eight hundred miles apart.^ In 

 1886 occurred the Charleston earthquake, an event still fresh in the 

 minds of most of our population. 



As to earthquakes of the several classes, the falling in of the 

 roof of a buried cavity causes slight shocks. Quakes of this kind 

 have often been reported from certain parts of Switzerland, the 

 Tyrol and elsewhere, but all have been local in character. It seems 

 certain too that the blocks falling in the caverns of southern Indiana 

 and Kentucky produced vibrations sensible on the surface, but re- 

 ports of such have not come under my eye. 



Earthquakes arising from volcanic explosions or associated with 

 eruptions form a much more important subdivision. Until within 



* W. H. Hobbs, " Earthquakes," p. 315, New York, 1908. 

 ° H. D. Rogers, Am. Jour. Sci., I., xlv., 342, 1843. 



