H. Warth — Origin of Limestone. 159 



of the sea avail anything. It exceeds in quantity that of the air, 

 but is still at the most equivalent to 7 centimetres of limestone 

 covering the earth's surface. Now the existence of animal life 

 throughout the sedimentary era implies that from the earliest times 

 the composition of the earth's atmosphere cannot have differed very 

 materially from the present one. Yet as carbon dioxide has been 

 continuously taken up by weathering igneous rocks, and also by 

 the production and storage of mineral, coal, etc., there must have 

 been a continuous renewal of the carbon dioxide contents to maintain 

 an equilibrium. The distribution of limestone throughout the whole 

 sedimentary era, and the alternate occurrence of coal of different 

 ages, leave no doubt that there has been a regular accession or renewal 

 of carbon dioxide from first to last. The only question we have to 

 answer is where this carbon dioxide was derived from. 



The amount of carbon dioxide as calcite and in the free state in 

 the solidified igneous rocks is far too little for the above purpose, 

 but there is ample evidence of a continuous supply by exudation 

 from deep-seated parts of the earth's crust. The gas issues either by 

 itself at isolated points in smaller quantity, or else in larger bulk 

 in certain volcanic regions. Much of it appears also in solution in 

 mineral springs. The possibility of a continuous supply is demonstrated 

 by the fact that fiery liquid lava is known to give up carbon dioxide 

 on its appearance at the earth's surface. It is thus clear that the 

 cooling and solidification of igneous rocks may be accompanied by 

 an issue of carbon dioxide gas, and this issue will be very regular, as 

 the process of cooling is also regular and practically constant. This, 

 then, is the source from which the atmosphere is supplied with 

 carbon dioxide, which is all the time utilized in the production of 

 limestone and dolomite, coal, bitumen, etc. 



To confirm this explanation it would be necessary to collect 

 statistics, firstly of all the stores of limestone on the earth's surface, 

 and secondly of the approximate issue of carbon dioxide. It would 

 be no small task to procure such data with any degree of accuracy. 

 Meanwhile a very rough estimate might be made, or should we 

 call it a guess, to serve the purpose of a test. If we assume the 

 accumulated sedimentary limestone of the earth's outer crust to equal 

 a bed 50 metres in thickness covering the land surface of the globe, 

 and if we fix the duration of sedimentaries containing organic 

 remains (animal) at fifty million years, we can easily calculate the 

 uniform issue of carbon-dioxide gas per second. This uniform issue 

 of gas equals at 760 millimetres pressure 2,500 cubic metres. 1 

 Considering the size of the earth we may rest satisfied that this 

 amount is at all events of the right order of magnitude, and that the 

 above hypothesis stands on a good foundation. We have thus before 

 us one more of the wonderful provisions for the persistent develop- 

 ment and maintenance of plant and of animal life on the globe. 



1 I find records in Bishop's Elements of Chemical and Physical Geology 

 showing that the mineral springs at Cannstatt yield one quarter of a cubic 

 metre of carbon dioxide per second. 



