xii The Crust of the Earth 229 



opening of great fissures, and other surface changes often 

 result from earthquakes, which may thus alter the course 

 of rivers and form or drain lakes. But the occasional 

 destruction of cities and houses, and the peculiar sensation 

 of terror and helplessness which earthquakes produce in 

 most minds, are apt to give an erroneous and much ex- 

 aggerated idea of the power of such shocks in forming the 

 scenery of the globe. The researches of Professor Milne 

 and other scientific men in Japan, and the extensive 

 use of seismometers or earthquake measurers, have 

 thrown much light on the nature of shocks and tremors. 

 The to-and-fro or up-and-down motion of the Earth in a 

 shock severe enough to throw down houses is probably not 

 much more than an inch. A model constructed by Pro- 

 fessor Sekiya (the professor of Earthquake Phenomena in 

 Tokyo) of the path described by a particle during the pas- 

 sage of an earthquake shock resembles a tangled hank of 

 twine. 3 It is the shaking produced by such a complex dis- 

 turbance rather than the actual lifting of the surface that 

 produces destructive effects. Some of the tremors detected 

 by seismometers are not produced by the internal energy of 

 the Earth. It has been proved in Italy that changes of 

 atmospheric pressure jar the elastic and sensitive crust ; and 

 in Japan a gale blowing against a range of mountains has 

 been found to set the greater part of the island quivering. 



302. Wrinkling of the Earth's Crust. The Earth 

 necessarily contracts as it cools, and the crust composed of 

 stratified rocks falls into wrinkles in order to adapt itself to 

 the reduced area of the globe, just as the skin of an apple 

 gradually becomes wrinkled in adapting ftself to the drying 

 and shrinking fruit. Reasons have already been given 

 ( 278) for believing that from a very early period the 

 Abysmal and Continental Areas have occupied their present 

 position, and probably they represent the troughs and crests 

 of the earliest Earth wrinkles. The primitive furrows 

 themselves must have disappeared as the crests were worn 

 away by erosion, and the resulting sediment was deposited 

 on the upper slopes of the hollows, to be consolidated in 

 turn and form part of a new set of wrinkles, which shared 



