970 A TREATISE ON METAMORPHISM. 



posed in the belt of weathering this carbon dioxide escapes. Since the 

 volume of the original and sedimentary rocks which have been broken up 

 into fine particles or decomposed so as to allow the major portion of the 

 gases to escape is very great, the amount of carbon dioxide given off to the 

 atmosphere from this source must be vast. 



In order to obtain any idea of the net gain to the atmosphere from 

 carbon dioxide liberated from occlusion, much more work must be done. 

 First, an estimate must be made as to the mass of the original igneous rocks 

 which have been broken down, and it must be ascertained how much 

 occluded carbon dioxide there is upon an average in these rocks in order 

 to compute the amount of carbon dioxide liberated. In the second place it 

 must be ascertained how much occluded carbon dioxide is in the secondary 

 rocks. Localty the sedimentary rocks are very rich in occluded carbon 

 dioxide in consequence of the process of silication and of the partial escape 

 of the liberated carbon dioxide. This carbon dioxide is indirectly derived 

 from the atmosphere. Third, a part of the enormous quantity of carbon 

 dioxide given off by volcanoes may be that originally occluded in the 

 centrosphere. The quantity of carbon dioxide of this origin must appar- 

 ently long, if not forever, remain a matter of conjecture. The total gain 

 of the atmosphere in carbon dioxide from occlusions is the sum of that 

 liberated from the original igneous rocks and that derived from magma, 

 less that held in the secondary rocks. 



It has been seen that various forms of carbon are subordinate original 

 constituents of meteorites. (See pp. 945-946.) Hence, another source 

 of carbon dioxide may have been the oxidation of the carbon contained 

 in meteorites and the exhalation from meteorities of carbon dioxide 

 originally contained in them in that form. However, the additions of 

 carbon dioxide derived from meteorites can hardly have been important 

 since the beginning of Algonkian time. Consequently this means of 

 restoring carbon dioxide to the atmosphere is of little consequence for 

 the period which we are considering, that in which the sedimentary rocks 

 were built iq:>. 



Another important source of carbon dioxide is the water ascending 

 from the zone of anamorphism. The amount of this carbon dioxide is 

 incalculable, but certainly it is very large. The gases included in hot 

 springs and in deep waters rising from mines are dominantly composed 



