PRIMARY FRACTURE PATTERN 165 



terials with the same perfection as in more ancient and far more rigid 

 rock-masses.^2 This is probably to be explained by a continuation of the 

 same system of stresses and strains within the earth's outer shell incident 

 to further contraction. Indeed, the study of the Pleistocene deposits of 

 Riigen has shown that block faulting is actually going on in them at the 

 present time.^^ Study of the New England region has likewise shown 

 that the glaciated rock surface has there been faulted in post-Glacial 

 times.^* The development of a remarkably perfect rectangular joint sys- 

 tem within the deposits of an old irrigation basin in the Syrian desert 

 (see plate 12, figure 1) offers evidence favoring the continued develop- 

 ment of joint systems into our own times. 



Deductions concerning the Nature of Faults 

 difficulties in the way of securing fault maps 



No study of faults could be considered in any degree adequate which 

 did not recognize that the faults proven to exist by the accepted methods 

 can represent but a small fraction of their actual number. Unlike folds, 

 which are open to inspection or to reconstruction whenever rocks outcrop 

 at the surface, faults by their very nature tend to bury themselves from 

 sight. Since de Beaumont's reckless but convenient use of imaginary 

 faults in order to explain the positions of mountain ranges, the geologist 

 who would guard carefully his reputation has been forced to restrict the 

 use of faults on his maps to those fortuitous larger displacements which 

 may be proven to exist by the observed lack of correspondence of the beds 

 which cross them. 



It seems to have been rather generally overlooked that since geologists 

 are required to color in their maps and prepare hypothetical sections 

 where continuous outcrops are not present, as great violence may be done 

 to the facts through the omission of faults which are probably present as 

 by their introduction where they do not exist. The significant fact is that 

 the geological map and section as prepared today call for the representa- 

 tion of the attitude of rock at every point on the surface, whether the 

 necessary data are available or not. It is this difficulty and the way in 

 which it has been met, which accounts for the occasional and seemingly 

 accidental introduction of the fault on geological maps. Theory and 

 experiment are in agreement in indicating that fault^^, like joints and 



"G. K. Gilbert: Monograph I, U. S. Geological Survey, 1890, ,,p. 211-213. Also I, C. 

 Russell : Monograph XI, ibid., 1885, pp. 162-163. 



■^3 Giinther : Loc. cit., pp. 58-60. 



''* J. B. Woodworth : Post-glacial faults of eastern New York. New York State Mu- 

 seum, Bulletin 107, 1007, pp. 4-28. See also G. P. Matthew : Movements of the earth's 

 crust at Saint John, New Brunswick, in post-Glacial times. Bulletin of the Natural 

 History Society of New Brunswick, No. 12, 1894, pp. 34-42. 



