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On a Figured Variety of Coal, occurring in the Coal-field of 

 Glamorganshire ; in a Letter to the Editor, — By J. Mac 

 CuLLocH, M.D. F.R.S. 



Dear Sir, 



I WAS not aware that the singular variety of coal, to which 

 the title of this letter alludes, was unknown to mineralogists, or 

 I should not so long have delayed sending you this notice of a 

 peculiarity, which, independently of the difficulty which it pre- 

 sents, offers a fact deserving of regard in the history of this 

 interesting substance. I must presume, that it has never yet 

 occurred elsewhere, than in the place whence the specimens, 

 which I have seen, were procured ; because a form so remark- 

 able could not have failed to attract the attention even of the 

 workmen, and would, therefore, have, ere now, been brought be- 

 fore the attention of mineralogists. Should it merely have been 

 overlooked in other coal deposits, the present public notice may 

 serve to call attention to it ; and, perhaps, also induce mine- 

 ralogists, as well as workmen, to examine more narrowly into a 

 substance, which, in spite of its importance and familiarity, 

 must have been strangely neglected, when such doctrines re- 

 specting its chemical nature, as those of Mr. Kirwan, and 

 respecting its chemical origin, such as those of Sir James Hall, 

 and Play fair, could have been received, without question, for so 

 long a time, and entertained as truth till they were corrected, 

 at so very late a period, by my own examination of bituminous 

 substances, appended to the Essay on the Distillation of Wood, 

 in the Geological Transactions. 



The variety, to which I allude, has been frequently found in 

 the coal works about Merthyr Tidfil, and, indeed, may be said 

 to occur almost daily ; but how widely it may extend through 

 this coal basin, there are no means of knowing. It would be 

 superfluous to describe, either the nature of this coal-field, or 

 of the coal itself, since both are familiarly known 5 it may be 

 sufficient to remind your readers, that it is a dry coal, though 

 not, in this respect, of a very highly defined character ; while I 

 hope that they are already aware, from the paper to which I 

 have alluded, that there are no definite varieties of coal, as is 

 commonly supposed, in consequence of certain Daisleading and 



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