Mr. C. Fox on tJie Construction of the Oblique Arch, 167 



notice, is not the only one in the island of Cuba where this 

 remarkable variety of coal exists. Nearly contemporaneously 

 with the discovery of the coal of Casualidad, it has been ob- 

 served about midway between the cities of Matansas and 

 Havana, not far from the sea-coast. If this be not a pro- 

 longation, at the distance of six leagues, of that we have 

 here described, it is an additional evidence of the great pre- 

 valence of bituminous matter in the serpentine and eupho- 

 tides of Cuba. The vein at this position has not yet been 

 worked, nor have mining operations been arranged at either 

 position. Some barrels of the coal from near Matansas have 

 been lately received at Philadelphia as specimens. 



We are not aware that any other of the West India islands 

 contain coal in sufficient quantity to be worked. In Jamaica, 

 it appears, on the authority of Mr. De la Beche, coal exists 

 in veins of an inch or two in thickness, occurring stratified 

 with the usual coal-measures and carboniferous rocks; but 

 these veins are too insignificant to be worth mining. 



Of the geology of St. Domingo we know very little, and 

 shall probably remain ignorant for a long time to come. 



It were an interesting fact, if it be as we conceive, that this 

 is the first discovery within the tropics, in this part of the 

 globe, of workable veins of remarkably pure coal. 



Philadelphia, Dec. 20, 1836. 



XXXIII. On Mr. Peter Nicholson's Rule for the Construction 

 of the Oblique Arch, By Charles Fox, Esq. 



To the Editors of the Philosophical Magazine and Journal, 



Gentlemen, 



TT AVING seen in your last Number (p. 75) a letter extracted 

 ^ -* from the Newcastle Journal, addressed by Mr. Henry 

 Welch to Peter Nicholson, Esq., in which he states " the 

 propriety of setting the public right as to whom the merit is 

 due, for a proper and certain rule for the construction of the 

 oblique arch," and subsequently says, " I think that there can 

 be no doubt, that your claim to the rule for the proper forma- 

 tion of the stones is prior to that of Mr. Fox, and I have 

 yet to learn that any rule exists by which the oblique arch 

 can be so truly built as the one which you have published ;" 

 I feel, therefore, bound in justice to myself, briefly to notice 

 it, and also because the principle laid down in my former 

 paper (vide vol. viii. of this Magazine, p. Si99) does not ap- 



