134 Dr. Mac Cwllocli on a Figured Variety of Coal. 



coal ; and it is one probably which has often prevented it from 

 being remarked, as it doubtless causes the specimens to appear 

 more rare than they actually are. The eye does not conjecture 

 ■where they are to be found ; or the blocks, which contain this 

 structure, are not different in aspect from the ordinary portions 

 of the stratum. It is only from casual fracture that they come 

 to light ; while many are destroyed every day in the act of 

 breaking up the materials for the coal hearths. If the fracture 

 has been fortunate, the block divides in the middle, parallel to 

 its stratified structure ; and, on separation, each piece is found 

 to contain the projecting figure which I have described ; the 

 ridge on the one-half fitting exactly to the vacuity in the other, 

 and admitting them to be refitted just as the fingers of two 

 hands may be so adapted. Occasionally, some adhesion oc- 

 curs between the opposite portions ; in which case a portion of 

 the ridge on one block is broken off; but I have seen speci- 

 mens of nearly a square foot in surface, where the whole was 

 absolutely perfect. This circumstance is the one to which I 

 referred above, as explaining the reason why the intervals be- 

 tween the ridges or curves, at the surface, were equal to the 

 breadth of the ridge at the base. The cut B represents a kind 

 of section of this fact. 



Such is the description of this singular variety of coal. I do 

 not pretend to explain it. There would be no difficulty in filling 

 a page with conjectures and hypotheses in the usual taste; but 

 while there is no analogy to which it can be referred, nor any 

 general law elsewhere, with which it can be associated, I can 

 see no purpose in such waste of words. It is not possible to 

 conceive how it can have depended on any animal structure, 

 for various reasons j nor are there any means of referring it to 



