OF THE MORE DISTURBED ZONES OF THE EARTH'S CRUST. 471 



witnessed in all districts of regular crust plications. The theory represent s 

 the cleavage dip as growing progressively steeper the nearer it is to the lines of 

 greatest igneous action, the facts in nature show that the cleavage, the folia- 

 tion, and the axis planes of the flexures, with which these are approximately 

 parallel, grow progressively steeper the farther they recede from those lines of 

 maximum energy. 



Concluding theoretical views. 



The wave-like structure of undulated belts of the earth's crust is attributed to an 

 actual pulsation in the fluid matter beneath the crust, propagated in the 

 manner of great waves of translation from enormous ruptures occasioned by 

 the tension of elastic matter. The forms of the waves, the close plication of 

 the strata, and the permanent bracing of the flexures, are ascribed to the 

 combination of an undulating and a tangential movement, accompanied by an 

 injection of igneous veins and dykes into the rents occasioned by the bendings. 

 This oscillation of the crust, producing an actual floating forward of the 

 rocky part, has been, it is conceived, of the nature of that pulsation which all 

 great earthquakes produce at the present day. 



11. Cleavage. 



The cleavage planes having been shown to be parallel to the axis planes of the 

 flexures, and locally to the planes of the great faults, and these being obviously 

 the belts of maximum temperature in a plicated district, it is suggested that 

 both cleavage and foliation are due to the parallel transmission of planes or 

 waves of heat, awakening the molecular forces, and determining their direction. 



VOL. XXI. PART III. 6 L 



