green's explanation of mediterranean zone 79 



day, and the constantly repeated stress would search out planes of weak- 

 ness in the crust, and might change them to fractures, as the constant 

 bending of a wire at last breaks it ; as a weak joint in a bicycle chain is 

 constantly strained as it goes over the geared wheel and at last broken. 

 As we now revolve the globe beneath the vertical wire, many northeast 

 and northwest coastlines, which are assumed to be fracture lines as well, 

 come under it. If we halt the globe so that Gibraltar is again beneath 

 the solstice, the Pacific coastline of Asia, the most remarkable and cer- 

 tain fissure line of all, comes under the line AB. Indeed, the whole band 

 of fire around the Pacific is nearly under this line. And it seemed to 

 Green that the maximum tidal wave thus regularly and repeatedly pass- 



Fiuure 6. — Diagram of the Globe placed so that F is in Solstice. 

 To illustrate tidal stresses. 



ing through this coastline where the slope changes so rapidly might 

 intensify any existing tendency and cause fracture. 



But the same tidal stress tends also to produce cleavage at right angles 

 to the above plane, and thus parallel to the ecliptic, EF. This stress de- 

 creases from equator to pole. There is set up a horizontal differential 

 strain between each element of the crust — that is, a narrow band nearest 

 the horizontal circle is stretched most, the next band above a little less, 

 and so on north and south, causing a tendency to rupture between the 

 bands. This force would also reach its maximum in the solstitial ecliptic 

 plane, as is indicated by the shading between EF and IJ, and might 

 search out planes of weakness on the earth's surface along great circles 

 tangent to the tropics. . 



