572 



SCIENCE PROGRESS 



grain to be wholly transposed, and the effect, being cumulative, 

 would not only allow the grain to travel onwards indefinitely, 

 but, all grains in the rocks adjacent being similarly affected, 

 the whole rock mass would move, and follow the direction 

 which the wave surface would take in a perfectly elastic 

 medium. This explanation of rock deformation accounts for 

 the existence of perfectly unaltered rocks between the origin 

 of the thrust which buckled the earth's crust, and the resultant 



C^ETow 



SCALE IN MILES 



Fig. i. 



mountain chain, and it provides an effect for the incessant 

 tremors which sensitive seismographs, like the bi-filar pendulum, 

 show are being propagated. 



In the south-western portion of South Africa we find a 

 very close imitation of Mr. Mellard Reade's sink, or rather, 

 one of the far corners of it ; the newer Cape rocks — the Neo- 

 afric beds, we may call them — rest on an older series, the 

 Pal-afric, in such a way that these latter form a right angle, 

 and they are further stayed by heavy intrusions of granite, 



