Geological History of the Atmosphere. 319 



Kingdom ; and if the world were better explored it is quite 

 possible that many large areas might be found to be very 

 much richer. 



The second objection is undoubtedly a strong one, and 

 probably applies with full force to the deep-ocean or abysmal 

 areas, which cover about 50 per cent, of the earth's surface. 

 But the ' transitional " areas, covered by water less than 

 6000 feet deep, may quite well be included in our calculation, 

 as they are regarded as coming within the sphere of ordinary 

 geological change; that is to say, the alternation from drv 

 land to sea-bottom and vice versa. At the very least they are 

 not too far from the land (and what formerly was dry land) 

 to contain thick strata of sedimentary rocks derived from 

 the land by ordinary denudation, and they may therefore be 

 expected to contain numerous rich deposits of coal. The 

 continental and transitional areas are estimated to make up 

 about 50 per cent, of the earth's surface ; and if they contain 

 as much coal and other carbonaceous matter as would be 

 equivalent to the whole of our free oxygen, then obviously 

 they must contain on the average double the amount that has 

 just been estimated for the United Kingdom, or as much as 

 would make a layer of eoal 5 feet thick over their entire 

 surface. 



But, on the other hand, it is quite possible that the above 

 estimate for the United Kingdom is much too low. The 

 total amount of carbonaceous matter thinly distributed 

 through many kinds of rock might be many times greater 

 than that collected into thick seams of coal ; and the same 

 principle might apply to the rest of the world as well. In 

 fact the proper way to state our question is to ask, not how 

 much coal is there in the world (using the word coal in its 

 ordinary acceptation), but what is the total amount of car- 

 bonaceous matter in the earth's crust? If we knew the 

 percentage of carbonaceous matter in all geological forma- 

 tions, or if we simply knew the average percentage in a 

 sufficient number of drilkcores, drilled to a sufficient depth 

 all over the earth, we might be able to give a fairly good 

 answer to the question. Many wells and bores have already 

 been drilled to great depths in many parts of the world, but 

 probably it is only in comparatively few cases that a definite 

 or perhaps even an approximate answer could be given if the 

 question were put as to what was the average percentage of 

 carbonaceous matter in the whole depth of the bore. No 

 doubt due note is taken of the general character of the rocks 

 passed through, but that of itself can give only a very rough 

 idea of the amount of carbonaceous matter present. I have 



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