produced by working Beds of Coal. 167 



as three seams of coal were successively worked away below. The tract of ground 

 alluded to is of a quadrangular figure, of about twenty-three acres in area, and is 

 crossed by a railway near its eastern or narrowest end. It is in the Marquis of 

 Londonderry's Pensher Colliery, in the county of Durham. 



The tract in question contains the following five seams of coal — see Section : 



Thickness. 



Depth below the 

 Surface. 



Ft. In. 

 1 8 



Fathoms. 



3 6 



62 



6 3 



73 



5 



83i 



3 8 



107 



1st. — The Three-quarter Seam 



This seam is not deemed workable at present. 



2. — The Five-quarter Seam 



3. — The High-main ditto , 



4.— The Maudlin ditto , 



5.— The Hutton ditto 



The three latter beds have been removed, and caused the subsidence of the sur- 

 face about to be described, and the Five-quarter is now in course of working. 



No. 3. The High-main seam was the first which was wrought in the pillars, and 

 was finished in 1829, when a settlement in the surface was noticed. This was 

 immediately discovered by the lowering of the railway, which required to be raised 

 to its original level. 



No. 4. The Maudlin seam was next wrought in the pillars and finished in 1831, 

 when a second settlement of the surface took place, and the railway had again to 

 be raised. 



No. 5. was then worked in the pillars and finished in 1833, when a third set- 

 tlement of the surface took place, which required the railway to be again raised to 

 its original level. 



The working of No. 2. commenced two years ago, but is not yet finished. When 

 the pillars are all worked out, I have no doubt that another settlement of the sur- 

 face will take place. 



The extent of each settlement was not measured, but I have lately ascertained 

 that the whole amount of the settlement of the surface by the three " mine-quakes" 

 was five feet six inches, — the aggregate thickness of the three seams which have 

 been worked out being fourteen feet eleven inches. This appears to be but a small 

 degree of subsidence, considering the thickness of the coal which has been taken 

 away. But as the railway, which is the gauge-line, passes near to one end of the 

 excavated tract, it may not be supposed to pass over the line of the greatest de- 

 pression. Indeed, on looking at the ground over the centre of the excavated tract, 

 it appears to be much more depressed ; but as there are no land-marks by which 



