134 



Recent mining exploitation has shown that the brown 

 coal seams are developed at or near the bottom of the 

 Tertiary formation. As a consequence of the dip to the east, 

 the brown coal formation comes to the surface, or nearly 

 approaches' it, in the Moorlands area. It is this fact that 

 has led commercial exploitation to especially favour this par- 

 ticular locality, for open-cut mining is thus made, possible, as 

 opposed to the more expensive method of winning the coal 

 by deep mining, entailing additional costs in labour, pump- 

 ing, and timbering. 



In connection with mining explora-tion, bores are now 

 being sunk at intervals of 300 yards, and even closer, in 

 places. This close boring is steadily accumulating a fund 

 of information invaluable for discussion of the contour of the 

 surface upon -which the Tertiary strata was laid down. Thus, 

 also, will much light be shed upon the question of erosion 

 intervals, if such do actually exist between the beds of the 

 Tertiary strata. But until all the bores can be referred to 

 the same datum level, which has not so far been done, final 

 statements in regard to the above must be deferred. 



In Ml'. Broughton's paper (5) reference is made to one 

 line of bores which he had related to the same datum level 

 by means of a dumpy-level traverse. As a result, he shows 

 that the floor of the Tertiary formation is slightly undulating 

 and the coal beds occupy the depressions in this old land 

 surface of low relief. On this evidence it is assumed that 

 the shallow basins containing coal are isolated by rises in 

 the floor of aUcient slaty rocks. 



These depressed basins may have been ponded areas in 

 the coal-forming period, where plant life thrived and was 

 preserved in sodden beds. Subsequent marine sedimentation 

 overlapped the lignite-filled basins and extended as a con- 

 tinuous sheet over much of the former old land surface. 



The very unequal thicknesses of brown coal met with in 

 the various bores is accounted for, at least partly, by such 

 an original accumulation in basins. But it yet remains to 

 be shown to what extent irregularities in the coal beds are 

 due to wash-outs of the nature of erosion by contemporaneous 

 streams. of the coal-forming period, which tracks would be 

 afterwards obliterated by silts rendered highly carbonaceous 

 from ligneous matter transported from erosion areas else- 

 where. This and the question of a general erosion interval 

 at the upper limit of the lignite beds, with its bearing also 

 upon the extent and distribution of the residual lignite are 

 matters to' be settled when the boring operations are com- 

 pleted. • ■ 



(5) Loc. cit. 



