OF THE MORE DISTURBED ZONES OF THE EARTH’S CRUST. 471 
witnessed in all districts of regular crust plications. The theory represents 
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. 
ll. 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 UI. 6.1L 
