THE CARBONIFEROUS SYSTEM. 697 



yds. ft. in. yds. ft. in. j yds. ft. in. yds. ft. in. 



Coal 2 I Coal (Whickam St.) - 200 



Rock measures - - 10 Rock measures - - 10 



Coal - - - 006 



Rock measures - - 4 



Coal ... 006 



Coal (Brock well) - 102 



Various rock measures - 50 2 

 Millstone grit. 



yds. ft. in. 



Total thickness of rock measures ... 350 6 

 Total thickness of coal - 15 2 3 



Mr. N. J. Winch gives the following enumeration of the different strata passed through 

 in Bigge's Main Colliery in the Newcastle coal-field, which shows the relative preponder- 

 ance of the rock measures over the seams of coal in thickness : 



ft. in. 



1. From the surface of the ground they sunk through clay to the depth of - - 102 



2. Through sandstone from thence -- -._ -42 6 



3. They then came upon the first seam of coal, but which had only a thickness of - 8 



4. From this seam to the thick bed called the High Main coal of the Tyne, they sunk through 



29 different beds of sandstone and shale, varying in thickness from 40 inches to 31 feet, 

 intevstrat'ified with 8 seams of coal from 5 to 18 inches thick, amounting together to - 418 2 



5. The High Main coal of the Tyne had here a thickness of- - - - -68 



6. From this seam they sunk further through 52 beds of sandstone and shale, varying from 5 



inches to 84 feet in thickness, interstratified with 19 different seams of coal from 2 to 37 



inches thick, and amounting together to - ... 503 2 



7. They now came upon the seam of coal called the Low Main coal of the Tyne, which had in 



this pit a thickness of - - - - 2 9 



8. And they sank beneath this through 10 different beds of stone, from 12 inches to 12 feet 



thick, and two seams of coal of 4 and 12 inches, making together - 82 



And giving a total depth of - ... - 1157 n 



Thus 125 different strata were passed through, only 32 of which were seams of coal, 

 and only 19 of these were capable of being profitably worked. The thickest bed of coal 

 in the Newcastle district, the High Main of the Tyne, does not exceed 6 feet ; this is 

 exceeded by abed in the Yorkshire coal-field, near Barnsley, which is 10 feet; but this 

 is again far surpassed by the south Staffordshire or Dudley coal-field, which contains 

 seams from 30 to 45 feet in thickness. In this latter case, however, the enormous thick- 

 ness seems to be rather made up of a number of beds divided by thin layers of clay slate, 

 than one continuous stratum. In general, except near to the surface, a seam of coal will 

 not pay the expense of working under a thickness of two feet. 



The position of the coal measures is occasionally very highly inclined, but commonly 

 they lie at a less angle, and often, as a whole, exhibit the appearance of a huge trough, or 

 basin. The next engraving represents this construction, a section of the Bristol coal-field, 

 extending from the Mendip Hills to the north-west of Bath, a distance of about twenty 

 miles. The regular basin^shape given to the strata in the section is not indeed that which 

 a perpendicular cutting into the ground of the district would expose, for many disloca- 

 tions and disturbances would appear ; but the general arrangement of the coal measures 

 of that locality, and in other places, shows the concave bendings indicated. This dispo- 

 sition is not peculiar to the coal series, but belongs more or less to all formations where 

 underlying strata or igneous rocks project in hills and mountains, though it has been 

 more particularly remarked in the carboniferous system, from that having been more 

 attentively searched for its important product. It is obviously due to an upheaving sub- 

 terranean agency, to the action of which the series of coal seams has been variously 



