Figured Variety of Coal, 133 



arising from the general flat surface of the block ofcoal, and 

 so^convoluted as to produce this figure on the plane. A section 

 of that ridge, across any part of its course, gives a wedge-like 

 form, as is shown at A ; the base being continuous with the 

 ordinary coal, and the edge, which has a sensible breadth, vary- 

 ing from the twentieth to the eighth of an inch, being serrated. 

 The face or plane of this convoluted wedge (if I may use such 

 a term) is striated, or apparently fibrous ; but, when broken, no 

 appearance of fibres is visible, the whole being undistinguishable 

 in aspect and character from the general block ; which is in no 

 way different from the ordinary coal of the same strata. Lastly, 

 in all the specimens which I have seen, the length of the wedge, 

 or the height of the ridge, is about an inch, perhaps rather 

 falling short than exceeding. With respect to the convolutions, 

 I must yet remark, that, while they are perfectly capricious and 

 uncertain, so as to differ in every specimen, they conform most 

 rigidly to a sort of law pervading the convoluted madrepores, 

 which may be called the law of avoidance, and for which, in 

 those corals, there is an obvious cause, arising from the design 

 of the animals by which it is constructed. The same law, and 

 for similar reasons, is found in the honeycomb ; but it will pro- 

 bably long remain a mystery why it should occur here, where 

 no apparent cause can be assigned. What I here allude to is, 

 that, however the curve may wander and be contorted, the 

 neighbouring one always follows at an exact distance, as far as 

 any single point is concerned ; though as this second, or any 

 other curve, may hold a very different general course, spaces 

 must occur which would be greater than the general interval, 

 which, for a reason that will presently appear, is equal to the 

 base of the wedge, or ridge, or somewhat more than a quarter 

 of an inch. Such intervals will be found occupied by straight 

 pieces, or other adaptations, in such a manner as always to 

 preserve this mixture of average distance and avoidance : just 

 as is familiar in the honeycomb, when the form of the hive 

 does not allow the whole to be fdled in a more regular and 

 continuous manner ; a proof, by the way, that bees do not 

 follow a fixed rule, or are not solely guided by what has been 

 idly and obstinately called instinct. 



I must now point out the only remaining singularity of thi§ 



