STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 107 



tained by the Ziegler process. The coke is 23 to 24 per cent., the 



watery constituents vary Httle from 63 but the tar is from 1.24 in 



the earthy to 2.87 in the woody material. The earthy coal yielded 



105.63 liters of gas whereas the woody material yielded only 97.55. 



The composition of the gas is 



-I. II, 



Carbon dioxide 38.59 50.86 



Carbon monoxide 16.80 10.60 



Hydrogen 18.90 1590 



Carburetted hydrogen 0.60 i.io 



CnHm 2.10 2.10 



Oxygen 0.60 0.30 



Nitrogen 22.60 17.70 



Sulph. hydrogen 0.21 0.74 



The tar-water of number L, the ligneous type, is acid, that of the 

 other is alkaline. The amorphous, more changed material has less 

 acetic acid and more nitrogen combined as ammonia, but the gas 

 shows great increase in carbon dioxide with decrease of carbon 

 monoxide. The results may not be wholly comparable, since the 

 lignitic, woody material may contain some constituents in greater 

 proportion than found in the amorphous peat; the former is conif- 

 erous wood while the latter was formed in great degree from plants 

 of wholly different type. 



Summary. — Before proceeding to consideration of the Tertiary 

 coals, it is well to summarize the facts recorded in the preceding 

 pages. 



1. The area of Quaternary and Recent peat deposits is appar- 

 ently greater than that on which carbon deposits were laid down 

 during any preceding period of similar duration ; yet it is but a 

 small part of the earth's surface, for there are vast spaces on which 

 no peat has formed since the Quaternary began, though much of 

 the peatless regions has been forested. 



2. Peat bogs vary in size from a few square feet to thousands 

 of square miles. The smaller deposits are due to filling of pools, 

 ponds or lakes by plant invasion, while the more extensive deposits, 

 those on coastal or broad rivers plains, originated, certainly in some, 

 probably in most cases, in small, isolated bogs, which became united 



