130 A TREATISE ON METAMORPHISM. 



(1) The openings which have great length and breadth as compared 

 with their width are those of bedding partings, of faults, of joints, and of 

 fissilitv. It is recognized that many of the fractures are exceedingly 

 complex. They are, indeed, in many instances a series of parallel or 

 intersecting fractures, forming a zone of brecciation. However, for such a 

 a zone, as a whole, the statement still holds that the openings have great 

 length and depth as compared with their width. 



Bedding partings are parallel to the layers. Since ground waters 

 very frequently follow formations, the bedding partings become important 

 factors in the promotion of flowage parallel to the formation This is 

 especially true of the contacts of formations of different character. These 

 contacts are places of maximum differential movements, of consequent com- 

 plex fracturing, and therefore of important openings and large circulation. 



In position the fault, joint, and fissile openings ordinarily have an 

 important vertical element, or at least traverse the beds. Frequently they 

 are nearly vertical, or traverse layers or formations at right angles. In 

 consequence of this they are very important factors in the vertical move- 

 ments of ground water. 



As to continuity, bedding partings are likely to be the most continuous; 

 faults come next in continuity, joints next, and fissile openings are those 

 that are least continuous. 



Bedding partings are likely to be continuous for long distances, and 

 because of this and their size (considered on pp. 137-138), they are fre- 

 quently important factors in the flowage of ground water." 



Faults may have very great continuity. Thrust faults of 15 kilometers 

 and more along the dip are known; and along- the strike faults may extend 

 for even hundreds of kilometers, although ordinarily their extent is much 

 less. From their great persistence and from the fact that they are likely to 

 cut across formations, thus frequently severing and displacing impervious 

 strata and consequently connecting porous strata separated by impervious 

 strata with one another, faults are of very great consequence in the flowage 

 of ground water. 



Joints are less extensive than faults, but they may extend across an 

 entire formation, or even across two or more contiguous formations. The 



«King, F. H., Principles and conditions of the movements of ground water: Nineteenth Ann. 

 Kept. U. S. Geol. Survey, pt. 2, 1899, p. 126. 



