FOLDINGS OF THE PICTOU COAL FIELD. 29 



goiug west, of from five to thirty feet, culminating at the " saddle " in one of about fifty 

 feet. These faults in some instances do not extend far from the axial line 



Taking those faults of the second class resulting from irregularities of the main 

 folding, they are usually oblique to its general course, and radiate from some point mark- 

 ing an interruption to the regular flexure. Such faults are not unfrequently small towards 

 the outcrop, and after attaining their maximum throw, diminish again, or present them- 

 seh'es as a series of small faults accompanied by irregularities in the seam, and changes 

 of dip. 



The practical importance to miners of a general knowledge of the structure of the 

 district they are operating in, should be more generally recognised than is usually the 

 case. Faults are encountered necessarily as part of the hazard of every mining enterprise, 

 but too frequently they are attacked with equal chance. The study of the extent of the 

 folding and uplifting forces, gives a clue to the dislocations marking their course, and 

 when once a fault is recognised as belonging to any fixed system, the next one opposing 

 the miner can be overcome with less labor. 



It need not be inferred from these remarks that the faults occurring in coal mines 

 always approach the vertical in their "underlie." Cases are noted where the pressure 

 ai>pears to have taken an almost horizontal -direction, as if the overlying measures had 

 been too thick or too loose to have all participated in the movement. Under these condi- 

 tions, the first result of the pressure is seen in one or more undirlatious of the coal bed 

 with a thinning of the seam, but no interrux^tion of its continuity. A more continued 

 pressure gives rise to what are known as " dirt faults," in which the seam is slightly 

 displaced and its contents broken and crushed. If the pressure be more abrupt, a flat 

 lying fault is the result, which sometimes presents the reverse of the miner's rules, which 

 are based upon the generally correct assumption, that the inclination of the plane of 

 fracture poiats to the position of the disrupted portion of the seam. 



Cases have been noticed where the pressure, acting through one or more beds of 

 sandstone harder and less yielding than the associated strata, has forced them oblic|uely 

 against a coal seam so as either to practically obliterate the seam over a considerable 

 width of ground, or to move it with a more or less defined fracture above its level, from 

 which point the scam gradually returns to its normal level and water course. 



This system of faulting is generally observed in seams lying at low angles. In those 

 more steeply inclined, especially where transverse foldings have taken place, they are 

 represented usually under two heads. Where the measures are hard and unyielding, the 

 seam is broken and confused for some distance ; but where they are soft, as in the presence 

 of shales, etc., a series of undulations compressing the coal into lenses are observed. The 

 compressed coal is frequently hardened, deprived of more or less of its volatile matter, 

 and retains few marks of its original lamination. 



From a consideration of the effects referred to in these notes as producing disloca- 

 tions, it may be gathered that, in any given locality, a fault may not exceed the length of 

 the flexure producing it, and must frequently be much shorter. The bearing of this on 

 the study of the structure of a district by a field geologist should always be borne in 

 mind. Deductions based on the prolongations of any transverse fracture are uncertain ; 

 the lines following the main flexures are, on the contrary, important clues in questions of 

 unconformably succeeding horizons. 



