596 STUDIES FOR STUDENTS 



ferential movements are along the longer limbs. Therefore the 

 cleavage develops in a corresponding direction, being nearly 

 parallel to the bedding on one limb of each fold and cutting 

 across the bedding on the other, steeply inclined or overturned 

 limb. As the area of outcrop of the steeper limbs is much less 

 than that of the more gently inclined ones, the fact that the 

 cleavage cuts the bedding on one side of each fold is very likely 

 to be overlooked. As a result of the greater mashing thus 

 developing cleavage or fissility the longer limbs of the folds are 

 thinned more than the shorter limbs. 



If for any cause cleavage be parallel to the bedding planes, 

 as these are apt to be sh .aring planes in the zone of fracture, 

 the predominant fissility would be likely to be parallel to the 

 bedding. The other direction of fissility would be transverse to 

 the bedding, and might have a wider spacing. The first might 

 be called fissility and the second joints. 



In another case, after a cross cleavage has developed and the 

 rocks have passed into the zone of fracture, the stresses may 

 result in the development of fissility along two sets of shearing 

 planes, one of them being controlled in direction by the cleav- 

 age, the other by the bedding. The more regular parting, par- 

 allel to the cleavage, might be called fissility, and the less regular 

 parting, parallel to the bedding, might be called either fissility 

 or joints, depending upon its closeness. Whether the intersect- 

 ing planes of fissility are at right angles to each other would 

 depend upon the inclination of the cleavage and the bedding. 



In regions of complex folding it is difficult to make accurate 

 general statements of the relations of cleavage and fissility to 

 bedding. However, as a result of the action of the various 

 forces, a bed has a definite strike and dip, and the cleavage and 

 fissility have definite relations to these. As there are rapid 

 variations in strike and dip in regions of complex folding, it is 

 to be expected that there will be variations in the directions 

 and character of cleavage and fissility. Certain of the specific 

 relations of bedding and secondary structures in regions of com- 

 plex folding have already been considered (pp. 347—349). 



