24?. 



are so just, and his satire so pointed, as to give me some appre- 

 hension for the fate of my present letter, when subjected to his 

 criticism and keen raillery. He reminds me of Dr. Halley's con- 

 jecture, that the world on which we dwell may have another habit- 

 able world within it, to which may be attached a system of sub- 

 terranean luminaries, resembling those which yield light to our 

 upper world, but necessarily moving within a smaller sphere*. He 

 sarcastically asks, whether our volcanoes are any thing but the 

 grand outlets of the furnaces, and our veins of bitumen any thing 

 more than the clogged-up chimnies of this inner world ? The dread 

 of criticism must not, however, deter me I have engaged myself 

 to the work, and therefore must not shrink. 



Having laid before you the several opinions which have been 

 published, respecting the formation of coal, and having found my- 

 self under the necessity of stating my suspicion of their insuffi- 

 ciency, to account satisfactorily for the origin of this substance, it 

 becomes a duty to offer any observations, which may seem to be 

 likely, in the least, to elucidate a subject involved in so much mys- 

 tery. But be assured that, whilst doing this, I am not ignorant of 

 the difficulties which surround me ; nor, knowing how considerable 

 these are, do I presumptuously expect to establish an impregnable 

 system. On the contrary, I fear, that many unforeseen, and power- 

 ful objections may arise, against opinions thus hazarded, on a 

 question which has been left in a great measure undecided, after 

 careful discussion, by men of eminent abilities. If, on the one 

 hand, I experience the mortification of differing from opinions 

 which have been generally received ; it is, on the other hand, highly 

 satisfactory to know, that this difference is so little, as, in some in- 

 stances, to consist merely in an extension, and in others, in little 

 more than a modification, of those opinions. Thus the explana- 



* Miscellanea Curiosa, p. 43. 



