1862.] on Coal. 511 



their employment in the coal-mines ; and that the total quantity raised 

 in 1860 amounted to no less than eighty-four millions of tons. 



Mr. Smyth then proceeded to describe the nature of the various 

 substances with which the coal is associated, referring to specimens on 

 the table from the field of South Yorkshire. Comparison was made 

 between the total thiclcness of carboniferous rocks or coal measures of 

 different districts, as well as between the total thickness of coal (in the 

 aggregate of the seams) ; and hence, it was shown, we have one reason 

 for not estimating the value of a coal-field merely by its area, as we 

 find it laid down in a geological map. Thus, the well-known Durham 

 field, with a thickness of measures of about 2000 feet, has a total thick- 

 ness of coal of 50 feet. The Derbyshire, 2000, and almost twice the 

 thickness of coal ; the North Staffordshire, 6000 feet of measures, and 

 1 30 of coal ; whilst the South Welsh and Saarbrucken fields exhibit 

 thicknesses of 12 to 15,000 feet, with a proportionate increase (espe- 

 cially in the latter) of coal. 



A second reason for mistrusting area as a criterion of the im- 

 portance of a coal-district, is the various forms into which the coal 

 measures have been thrown or moulded by agencies operating at a later 

 date in the earth's crust, whence some districts may exhibit by outcrops 

 an indication of the full amount of their entire contents, whilst in 

 others the beds pass with a gradual inclination beneath newer for- 

 mations, through which they may nevertheless be accessible. As 

 instances of this were quoted, the vast accession of mineral wealth 

 added, even in the last twelve years, to the Westphalian coal-field, 

 by the explorations carried out through the covering of cretaceous 

 rocks which clothe the northern side of the coal-field, and the remark- 

 able pit lately completed by the Duke of Newcastle, at Shireoak, 

 which, commenced at a distance of several miles from any visible 

 coal-measures, pierced the new red sandstone and magnesian limestone, 

 and reached the "top-hard" coal at 515 yards in depth. 



Mr. Smyth then described certain physical features produced in the 

 coal seams subsequently to their consolidation, such as the cleat and 

 backs, or various nearly vertical divisions, often more or less filled 

 with carbonate of lime or iron pyrites, which add greatly to the 

 amount of ash and clinker. 



In referring afterwards to the principal families of plants which are 

 found either in, or associated with, the coal, he wished to show that 

 their occurrence throws a light on the origin of the coal-seams, which 

 again becomes an important guide in enabling us to judge of the con- 

 tinuity of various fields, a question fraught with vital importance, in 

 consequence of the rapid rate at which some of them are being ex- 

 hausted. Thus the position of the stigmaria in the under-clay or floor 

 of the seam, and of the stems of sigillaria, lepidodendron, calamites, 

 &c., in the roof strata, point to the probability of the growth of the 

 vegetable matter in situ. The existence of numerous upright stems, 

 and especially those occurring so often and so dangerously to the miners 

 in the roof of certain coals, is a strong confirmation of the gradual 



