Mr. J. Phillips on the Lower Coal Series of Yorkshire. 349 



indistinctness of vision; the one, when the indistinctness arises 

 from undue scattering of the rays of light, — the other, when it 

 is owing to the chromatic aberration of white light. 



3rd. The organ excited in both cases is the brain; but 

 whether, being thus excited, it does not also excite some other 

 auxiliary organ, as in the case of the adaptation to different 

 distances, does not yet appear. 



4th. The actions excited are directed to the effect of remov- 

 ing, more or less, the exciting cause, and producing distinct 

 vision. 



Fochabers, 20th June, 1832. 



Note. — An investigation of the remarkable phsenomena de- 

 scribed in the preceding ingenious paper, but leading to results 

 different from those obtained by the author, will be published 

 in the next Number of this Journal. — D. B. 



LXV. 0« the Lcwcr or Ganister Coal Series of Yorkshire. 



By John Phillips, F.G.S., Sec. Y. P. S., Assist. Sec. Brit. 



Association, ^-c* 

 THHE lowest portion of the Yorkshire coal strata resting 

 -*- upon the millstone grit, produces comparatively but a 

 small quantity of coal, and this, in general, not of a good 

 quality. But no part of the coal-field is more curious in its 

 geological relations, or more worthy of close studj' by those 

 who desire to penetrate into the history of the production of 

 coal. We may define this lowest coal series very simply, by 

 saying that it is included between the millstone grit of Bram- 

 ley beneath, and the flagstone of Elland above, having a 

 thickness of about 120 or 150 yards, and inclosing near the 

 bottom two thin seams of coal, one or both of them workable, 

 and several other layers scattered through its mass, too thin 

 to be worth working. The most regular and continuous of 

 all these coal seams reaches, in a few places, the thickness of 

 27 or 30 inches, but is generally only about 16 inches. It is 

 worked at Yeadon, Rawdon, and^ Horsforth, near Leeds'; at 

 Baildon, and Heaton, near Bradford; Catharine Sluck, and 

 Swan Banks, near Halifax ; BuUhouses, near Penistone ; and 

 at several points about Sheffield. 



It would have been impossible to have traced so thin a seam 

 of coal along so extensive a range without some peculiar facili- 

 ties, — some points of reference more distinct than the varying 

 quality of the coal, and the still more irregular fluctuations of 

 the sandstones and shales. This coal seam is covered by a 

 roof unlike that of any other coal bed, above the mountain 



* Head I)cforc the Yorkshire Philosophical Society, October 2, 1832; 

 and communicated by the Council of that Society. 



