98 
SYMMETRICAL STRUCTURES OF ROCKS. 
The jointed structure thus investigated is an essential and neces- 
sary part of the structure of rocks, not to be viewed in the light of 
geological accidents, depending on subterranean movements, but afford- 
ing evidence by the constancy of its direction in large districts, 
of the action of some very general cause, capable of controuling the 
consolidation of the rocks so as to cause the separation of the con- 
densed masses along certain parallels. If this be not really crystal- 
lization, it is to be considered as a symmetrical aggregation of the 
molecules. The subject will again come under review, and it is only 
necessary now to observe that the direction of the joints is independent 
of at least all the minor faults and dislocations of the strata, which 
are altogether phenomena of subsequent origin. 
The following diagram represents the result of the investigation 
by breadths of shade corresponding to the frequency of long joints or 
fissures, parallel to each radius. 
