660 GEOLOGY. 



III. The More Remote Sequences of the Deformation. 



Effects on the constitution of the atmosphere and hydrosphere. — It seems clear 

 that if the contact of the atmosphere with rocks upon which it acts chemic- 

 ally were increased several fold, it would be robbed of its active constituents 

 at a markedly increased rate. Chief among these active constituents is car- 

 bon dioxide, which unites with the silicates to form carbonates, and with the 

 simple carbonates to form bicarbonates. The bicarbonate of lime in particular 

 is thus formed, and, as the bicarbonate is much more soluble than the mono- 

 carbonate, its formation is the usual means of solution of limestone, and of its 

 removal to the sea. Oxidation is next in order of activity. Starting with acceler- 

 ated oxidation and carbonation, a series of complicated actions followed which 

 are thought to have resulted in loss to the atmosphere and gain to the ocean. 

 The present state of science does not permit these to be traced out with full con- 

 fidence, but a sketch of some of the probable actions will serve to indicate the 

 nature of the problem involved, and give some hint of its intricacy. 



With little doubt it would be a serious error to start with the assumption 

 that the atmosphere and ocean, when the deformation took place, had their 

 present constitution. It is necessary, therefore, to consider at the outset what 

 may have been the nature of the atmosphere and hydrosphere before the Per- 

 mian deformation began to work changes in them. This leads us incidentally 

 to consider certain radical questions that relate not only to these particular 

 periods, but to similar periods when the land was low and limited, and great 

 limestone deposition, and sometimes coal formation, took place. The two cases, 

 great limestone deposition correlated with extended seas and low and limited 

 lands, and great coal deposition, are not identical, though sometimes measurably 

 combined. The Subcarboniferous period will be taken as the basis for con- 

 sidering the former, and the Carboniferous the latter. 



The atmosphere and hydrosphere in the Mississippian and Carboniferous periods. 

 — The facts that there was glaciation in low latitudes in the early Cambrian 

 or pre-Cambrian, that there was pronounced aridity in the Silurian in regions 

 where precipitation is now ample, that there had been active aerial life for 

 some time previous, and that 'the respiratory organs of both plants and ani- 

 mals were strikingly similar in nature and proportions to those of recent times, 

 combine to restrain us from assuming that the atmosphere, in any of the Paleo- 

 zoic periods, was radically different from what it is now; but still certain moder- 

 ate variations are not only compatible with these facts, and all other known 

 phenomena, but seem to be required by the phenomena whose interpretation 

 is here sought, as well as by theoretical considerations. The tracing out of 

 these variations is apparently essential to the solution of the problems of these 

 and similar periods. 



The part played by the limestone formation. — During the Subcarboniferous 

 period, a large deposit of limestone took place, the carbon dioxide of a part of 

 which was undoubtedly derived from the atmosphere. While no accurate esti- 

 mate of the amount of this limestone is now possible, it is certain that the total 



