1874] 



285 



[Stevenson. 



To give all the details leading to the conclusion offered by Prof. Jukes, 

 would be impossible here. I therefore present only a few sections, 

 showing the variations of a single bed within a limited area, sections ob- 

 tained in such proximity to each other, that no possible doubt remains 

 respecting the identity of the coals : 



Flying- reed Coal,. 



Interval, 



Thick Coal, 



1 







25'4" 



4' 

 10'6' 



25'4' 



4'8" 

 45'9" 

 22'Q" 



55'4" 

 24'3" 



G 



2'6' 

 118' 

 24' 



3' 

 128' 



22'8" 



Further sections* show that the Thick Coal finally breaks up into nine 

 beds, the whole occupying, with the intervening rocks, a vertical space 

 of 390 feet. The sections given above show that, within a distance of 

 less than one mile, the interval between the two benches of the seam in- 

 creases from zero or a very thin parting to 128 feet. The extent of area 

 forbids the supposition that this occurred in a petty lagoon. It is, as I 

 hope to show hereafter, in full accordance with the law of coal deposition 

 in our own country. 



Other instances might be cited from Great Britain. Thus Mr. Green- 

 oughf states that near Ashby de la Zouche, the bend, separating the 

 second and third seam of coal, is in the easternmost coal-pits, thirty-three 

 yards thick ; in the next toward the west, twenty-flve ; in the most west- 

 ern, only fourteen ; and that in the Budworth Collieries, half a mile 

 further toward the west, it vanishes entirely, the two seams runniug 

 together. Another instance is mentioned by Capt. Portlock in his report 

 on Londonderry, etc., pp. 600-601. 



In our own country, such marked illustrations though rare, are by no 

 means wanting. The bifurcation of the Mammoth Coal Seam is a well 

 ascertained fact and susceptible of absolute proof. At Mahanoy City, 

 Pennsylvania, one of the most important beds divides, and its branches 

 can be traced for a considerable distance, rapidly diverging. On the 

 Great Kanawha Kiver, in West Virginia, as I have shown:]: the celebra- 

 ted seam worked at Coalburg, shows this tendency to divide. At the 

 east end of the property of the company these partings are thin, rarely 

 exceeding three inches Followed westward, they increase, until at the 

 western boundary of the property the lower one is two feet thick. About 

 ten miles further down the river, three thin coals are found occupying the 

 horizon of this bed. In all probability, they are simply the subordinate 

 coals, separated by the greatly thickened partings. Cases of distinct 

 division of coals, attended by marked divergence of the benches, must 



* For the sections given above, see The South Staffordshire Coal Field, l)y J. Beete 

 Jukes. 2d Edition, 1859, pp. 87 and 38. 



\ A Critical Examination of the First Principles on Geology, 'by G. B. Greenough, 

 President G. S., &c., 1819, p. 22. 



X Annals of Lyceum Nat. Hist., Vol. X, p. 276. 



