434 Miscellaneous. 



we examine the composition of the ashes of coal, and that of the 

 fire clay, we discover the same ingredients in both. Potash, and 

 magnesia are contained in the fire clay, and from their constant 

 presence in coal appear to have been indispensable to the develop- 

 ment of the plants constituting it. 



This underclay may then be viewed with every probability, as the 

 soil in which the plants grew ; and the adaptation of such a soil 

 to the plants was obviously due to its alkaline constituent. These 

 primeval plants would not exhaust a soil so rapidly as those of the 

 present day ; for they invariably contain a much smaller quantity of 

 inorganic ingredients ; and their roots being but imperfectly deve- 

 loped would not furnish much excrementitious matter to the soil. 

 Once admit that an excess of carbonic acid was in the air during 

 this period, and an immense vegetation would be the result. The 

 carbonic acid being once extracted could only be returned to the 

 atmosphere by a complete decay of the plants which had' used it as 

 food. But we find that the plants constituting coal have been sub- 

 jected only to partial decay. They have yielded up most of their 

 oxygen, but their carbon has been for the most part retained ; their 

 hydrogen has also in a great measure disappeared. From the com- 

 position of coal compared with that of woody fibre, it is obvious 

 that during the formation of 800 cubic feet of Newcastle splint coal, 

 the atmosphere must have received 800 cubic feet of oxygen gas, 

 and lost a corresponding quantity of carbonic acid. Now, suppose 

 we were to calculate the quantity of carbon in all the carboniferous 

 deposits at two thousand billion pounds (a quantity which must be 

 much under the truth) ; then during its formation no less than 

 64,000,000,000,000,000 cubic feet of carbonic acid must have been 

 extracted from the atmosphere, and a like quantity of oxygen gas 

 returned to it.* This is equal to |ds. of the quantity of carbonic acid 



* 1000 lbs of charcoal in burning produce have 32,000 cubic feet of carbonic acid. 

 1000=32,000, or 1=32 : 2,000,000,000,000,000 lbs. will produce 64,000,000,000,000,000 cubic 

 feet. 



2,000,000,000,000,000 lbs. 



221Q lb =892,85^,142,057 tons. 



But the assumed number, 2,000,000,000,000,000, is impirical, and we have, therefore, to shew 

 it is not above the truth, however far it may be below it. Now we have already seen that 

 Manchester by fuel, for domestic purposes alone, sends into the air, every year, 23,614,285,714 

 cubic feet of carbonic acid. And, taking its manufactories into the calculation, we may 

 safely suppose, that the total amount will not be less than 46,000,000,000. Now— 

 64,000,000,000,000,000 



40,000,000,0~00 =1,391,304 



