THE PATH OF EVOLUTION 



as well in its union with hydrogen water which the 

 hot metals might decompose, as with the uncombined 

 oxygen of the air, diluted by the chemically indif- 

 ferent Nitrogen, with which it is mechanically mixed 

 but not chemically united. 



Carbon, which in its first molecular condition was 

 probably combined with Silicon, with Calcium or 

 with the other metallic bases of the earth, as carbides, 

 would next possibly unite with the oxygen or water, 

 to form at first Acetylene, Methane, Ethane, or other 

 carbo-hydrides, then later, with access of air, by com- 

 bustion forming Carbon Dioxide, setting silica, or 

 calcic hydrate, free ; perhaps also permitting the 

 formation of Petroleum, while free oxygen was yet 

 excluded from the nascent carbo-hydrides. The carbon 

 dioxide formed would escape into the atmosphere. 

 The farther cooling of the earth would permit the 

 luxuriant growth of vegetation that, absorbing the 

 carbon dioxide into plant tissues have ultimately 

 yielded us the coal measures the geologic condi- 

 tions permitting also the formation of the limestones 

 of the same measures from the calcic and magnesian 

 hydrates arising from the parent carbides : thus 

 explaining in part the massive occurrences of calcic 

 and magnesian carbonates in the Dolomites and 

 other mountain ranges, whose immense deposits seem 

 to require a geogenic theory for their primary occur- 



204 



