386 PALEOZOIC SYSTEM OF ROCKS. 



A portion of this circulating matter, in its course downward from the 

 organic to the mineral kingdom, stopped half-way, and was accumulated 

 as great beds of coal — reservoirs of stored force. As circulating water 

 descending seaward is stopped and stored in reservoirs to complete its 

 descent under the control of man, and do his work ; so circulating or- 

 ganic matter descending is stopped and stored, and is now completing 

 its descent under the control of man, and doing his work, and thus 

 becomes the great agent of modern civilization. 



A second portion of circulating organic elements completes its de- 

 scent, but in doing so accumulates iron-ore, the second great civilizer 

 of the human race. 



A third portion also completes its descent, but accumulates neither 

 coal nor iron-ore ; but it accomplishes a work far more subtile and 

 beautiful than either of the others. As each particle of organic matter 

 returns to the atmosphere, it compels a particle of mineral matter to 

 take its place, thus completely reproducing its form and structure. 

 Thus fossils are formed, and thus is the history of the organic kingdom 

 self-recorded. Thus, while the other two portions have subserved the 

 material wants of man, this portion has subserved his higher intellect- 

 ual wants. 



Bitumen, Petroleum, and Natural Gas. 



The origin of bitumen and petroleum is so closely connected with 

 that of coal, that although not confined to, nor even found principally 

 in, the Coal-measures, the subject is best taken up in this connection. 



It is well known that coal or any organic matter, by suitable distil- 

 lation, may be broken up into a great variety of products : some solid, 

 as coal-pitch ; some tarry, as coal-tar ; some liquid, as coal-oil ; some 

 volatile, as coal-naphtha ; and some gaseous, as coal-gas. Now, we find 

 collected, in fissures beneath the earth, or issuing from its surface, a 

 very similar series of products : some solid, as asphalt ; some tarry, as 

 bitumen ; some liquid, as petroleum ; some volatile, as rock-naphtha ; 

 and some gaseous, as marsh-gas of burning springs. There can be no 

 doubt that these also are of organic origin. The utilization of all 

 these products, especially petroleum and gas, have now become a great 

 industry. 



Geological Relations. — Bitumen and petroleum are found in all fos- 

 siliferous rocks, from the lowest Silurian to the uppermost Tertiary, 

 under certain conditions, among which are the local abundance of or- 

 ganisms from which these substances are formed, and the absence of 

 great metamorphism. The signs of their presence in any locality are 

 iridescent scums on the water of springs (oil-show), and the issuing of 

 combustible gases (burning springs). In regard to the first sign, it 

 must be remembered that iridescent scums are produced by many other 

 substances besides petroleum. The second sign is considered the best, 



