308 THE BORDERLAND OF SCIENCE. 



one ton per human being, the supply would last for 

 that enormous period. 



But let us consider what portion of this vast supply 

 falls to the share of this country not including, of 

 course, those coal-fields which lie in countries forming 

 British territory, but not forming part of the British 

 Isles ; and let us compare our store of coals with our 

 present rate of consumption and with the probable 

 rate of consumption during coming years. 



Some difficulty arises at the outset in determining 

 what portion of the coal-fields actually existing in the 

 British Isles may be regarded as available. We might, 

 indeed, render the question more complicated by setting 

 as a necessary part of the inquiry the determination of 

 the actual expense per ton for mining, carriage, and so 

 on, according as different parts of the coal-fields were 

 being worked. But for obvious reasons this would 

 not be the place for dealing with the subject in so 

 general or so complete a manner. The sole point I 

 shall here touch on, as bearing on the availability of 

 the various coal-stores, is the probable depth to which 

 coal-mining operations can be pushed. 



It was held by many, ten years ago, that the coal- 

 mines might be- worked to a depth far exceeding 

 the greatest which had then been reached. ' The 

 difficulties in the way of deep mining,' wrote Mr. 

 Leonard Lemoran, Surveyor of Mines, c are mere ques- 

 tions of cost. It is important to notice that the 

 assumption of 4,000 feet as the greatest depth to which 

 coal can be worked, on account of the increase of tern- 



