88o 



STUDIES FOR STUDENTS 



perpendicular, and their bottoms are occupied, not by a stream, 

 but by an accumulation of great angular blocks composed of 

 the same material as the walls. Deep below this accumulation 

 of blocks one may sometimes thread his way until the ice and 

 snow of the preceding winter are found unmelted even at the 



end of summer. Such 

 gorges find their sim- 

 plest explanation in the 

 local depression of a 

 long and narrow oro- 

 graphic block along 

 vertical joint walls 

 (Graben), with the ac- 



Fig. 6.— Cross-section of fault-gorge (so called COmpaniment of much 

 " ice-gorge ") near Hartsville, Mass. The stippled fracturing and disloca- 

 area represents snow and ice. tion ; n the block itself. 



(See Figs. 6 and 7). 



1 1 . Arrangement of surface spri?igs in right lines. — Since the 

 time of Daubeny and Forbes the locations of springs have been 

 connected with fissures. Peale in his report upon the mineral 

 waters of the United States cites many regions where springs are 

 arranged along fault planes, and, speaking of the Great Basin, 

 says : "A map of the hot springs of the Great Basin would be, 

 to a great extent, a map of its displacements." 1 Regions might 

 be multiplied where essentially the same facts have been observed. 



NATURE OF EVIDENCE FOR ESTABLISHING A SYSTEM OF FAULTS. 



Observed faults are in parallel and biters ecting series — Having 

 made out within a region the presence of a number (larger or 

 smaller) of normal faults, it is next to be determined whether 

 they stand in any relation to one another If a considerable 

 number have been observed, it is likely that some will be found 

 to be parallel, or as nearly parallel as the errors of observation 

 allow. Evidence of this nature is, however, valuable in propor- 



1 Peale, Fourteenth Ann. Report U. S. Geol. Survey, 1894, P art H> PP- 3> °4; 

 see also Russell, Fourth Ann. Report U. S. Geol. Survey, 1884, p. 452; Hill and 

 Vaughan, Eighteenth Report, ibid., 1898, Part II, Plate XLVI; HoBBS, Twenty -fin* 

 Report, ibid., Part III, pp. 91-^?. 



