1909-] THEIR CAUSES AND EFFECTS. 251 



and the City Hall at Santa Rosa. The main source of the earth- 

 quake is thought to have been situated at a considerable depth below 

 the surface (Omori). 



(Lantern slides were shown to illustrate the destruction of 

 buildings in San Francisco, Santa Rosa and Leland Stanford Jr. 

 University, and the geologic and topographic changes wrought in 

 the surface of the ground along the line of fracture.) 



The Kingston Earthquake. 



The Blue Mountains, rising 7,400 feet above the level of a sea 

 18,000 feet deep, form the back-bone of the island of Jamaica. 

 They trend northwest-southeast and, according to Robert T. Hill,^* 

 from the earliest axis of folding now apparent. Upon this have 

 been super-imposed later east-west flexures corresponding with the 

 crustal movements that early in the Mesozoic era determined the 

 chief characteristics of the Greater Antilles. Charles W. Brown,^^ 

 reports observing " transverse faults in the Blue Mountain region 

 which undoubtedly indicate lines along which fractures may occur." 

 Professor Hill assumes an east-west axis of folding with an anti- 

 cline producing the trend of the Greater Antilles and leaving a 

 parallel syncline coinciding with the Bartlett Deep just north of 

 Jamaica. 



Such strong relief coupled with folding indicates a high state of 

 tension in the earth's crust. Resistance to stress is diminished on 

 steep slopes, especially when the application of pressure to the ends 

 of an axis is not made in the same plane, giving rise to torsional 

 strains. Fracturing results, tending to follow old fault planes, and 

 these fault planes were originally determined by zones of weakness 

 in the rocks. Fracturing, as we have seen, produces earthquakes. 

 Montessus de Ballore acquiesces in the folding postulated by Hill 

 and embraces the Greater Antilles, including Jamaica, within the 

 great Alpine geosynclinal. The region experiences frequent shocks 

 and one of the most dreadful disasters of modern times occurred 

 within it in the year 1692, when, as a result of an earthquake, the 

 greater part of Port Royal, the capital of Jamaica, sank into the 



"5h//. Mus. Comp. ZooL, Vol. XXXIV., p. 164. 



^^ Popular Science Monthly, Vol. LXX., p. 385, May, 1907. 



