338 president's address. 



Tlie Coal Measures are divided into three series, namely : 



1st. The Upper or Eed Ash Series. 



2nd. The Pennant Series. 



3rd. The Lower or White Ash Series. 



The first of these is about 3,000 feet in thickness, near 

 Swansea, and about 400 feet in the so-called " South Trough." 

 The average thickness of coal in this series is something over 

 66 feet, in some districts it increases to as much as 90 and 100 

 feet. 



The second, "Pennant" Series, varies in thickness from 

 1,500 to 2,800 feet. In it are several good seams of coal, 

 amongst which are the well-known Nos. 1, 2 and 3 Phondda, the 

 last so remarkable for its coking properties, The average 

 thickness of coal in this series is perhaps about 45 feet, but the 

 variation in different districts is very considerable. 



The Lower or White Ash Series is separated from the 

 Pennant by a hard Quartzy Rock known as the Cockshor Rock ; 

 it varies in thickness from 2,000 feet near the South crop to 500 

 feet on the East of the Coalfield. In this series are several 

 valuable seams of coal varying in thickness from 2 feet up to 

 even 10 and 12 feet, the total average thickness of coal being 

 from 50 feet in some districts to 70 feet in others. The 

 celebrated steam coals of the Rhondda and Aberdare Valley 

 belong to this division, and in it, too, is found the Iron Stone 

 ground, which in past years was of such very great value to the 

 iron manufacturers of South Wales, 



The Coal Measures have been subjected in past ages to the 

 vast upheavals of nature, in the same way as other geological 

 formations ; these have caused what are technically called 

 "faults," producing large and small dislocations of the Strata. 

 Some of these displacements are as much as from 200 to 600 

 fathoms. There is a large anticlinal ridge passing through the 

 Coalfields and dividing it into two troughs, the north and the 

 south trough. The seams on the south crop of the south trough 

 are highly inclined, lying in places at as steep an angle as forty 

 five degrees. This anticlinal has had the effect of enabling 

 seams to be continued to be largely worked which otherwise 

 would have passed to an unworkable depth. 



