NATURE OF FAULTS 167 



as he says, "the constanc}^ of the orientation over large areas has already 

 been confirmed/' are the necessary prerequisites to the formation of faults, 

 adding, "in many countries joints may be seen passing by various inter- 

 mediaries into faults properly so called." "'^ 



In the working out of the properties of joint systems a pioneer role 

 had already been taken by the early English geologists, especially John 

 Phillips, '^*^ Samuel Haughton,^'^ and Eobert Harkness.'^^ The dominance 

 of vertical planes, the uniform occurrence of parallel and intersecting 

 series, the subequal space intervals, the so-called "conjugate" rectangular 

 sets of master joints, and, lastly, the similar orientation of any series 

 over broad areas ; these are all either recognized or proven in practically 

 all of the papers. Haughton further showed that there was a system of 

 faults in the district which he studied, and that this was oriented in con- 

 formity with the local joint system. His studies are open to the criticism 

 that he averaged a wide range of joint direction in determining the pre- 

 cise azimuth of each series, but the essentially rectangular intersections of 

 the series is apparent. This elaborate and important pioneer study has 

 been often neglected by later writers on the subject, and it is evident that 

 Daubree was not familiar with it. 



The same dependence of faults on preexisting joints was shown in inde- 

 pendent studies made by Brogger in 1884 in the neighborhood of the 

 Langesimdf jord in Norway, "^^ and by the writer in the Pomperaug Valley 

 of Connecticut in 1899.^^ To quote from the last mentioned paper : 



"At the northern end of the eastern Orenaug twin, even smaller dislocations 

 than those just described may be observed. In fact, tlie dislocations here 

 appear in such numbers and are apparently of such small displacement that 

 they may be properly designated joints. The fracture planes, which are dis- 

 tant only a foot or two from one another, have strikes corresponding with the 

 faults observed elsewhere in the region. There seems, therefore, to be every 

 gradation from faults whose displacement measures hundreds and perhaps a 



" Daubree : G^ologie exp^rimentale. Paris, 1879, p, 304. 



■^•^ John Phillips : Observations made in the neigliborhood of Ferrybridge in the years 

 1826-1828. Philosophical Magazine and Ann. Phil., 2d ser., vol. 4, 1828, pp. 401-409. 

 Illustrations of the geology of Yorkshire ; part 2, The limestone district. London, 1836, 

 pp. 90-98. Manual of Geology (Etheridge and Seeley edition), London, 1885, pp. 83-84. 



" Samuel Haughton : On the physical structure of the old red sandstone of the county 

 of Waterford, considered with relation to cleavage, joint surfaces, and faults. Trans- 

 actions of the Royal Society of London, vol. 148, 1858, pp. 333-348. On the joint sys- 

 tems of Ireland and Cornwall, and their mechanical origin. Ibid., vol. 154, 1864, pp. 

 393-411. Also Quarterly Journal of the Geological Society, vol. 18, 1862, pp. 403-406. 



'^^ Robert 11. Harkness : On the jointings in the Carboniferous and Devonian rocks in 

 the district around Cork, and on the dolomites of the same district. Quarterly Journal 

 of the Geological Society, vol. 15, 1859, pp. 86-104. 



'» BrOgger : Loc. cit., see extract on p. 158 of this paper. 



8» Twenty-first Annual Report of the TJ. S. Geological Survey, pt. ill, pp. 114-115. 

 See also Journal of Geology, vol. 10, 1902, pp. 867-868. 



