INFLUENCE.OF LIMESTONE UPON THE ATMOSPHERE 621 
epochs when neither the one nor the other were greatly prepon- 
derant is not only not questioned, but will, in a separate ebaalel Con 
be urged as the special agency of an important function in bio- 
logical, as well as geological, progress. 
Other limitations will suggest themselves, as the change of 
calcium carbonate into calcium sulphate, and the reverse, in the 
sea or in the course of organic processes, but it is believed that 
none of them radically affect the particular function herein 
assigned to great epochs of limestone formation. 
T. C. CHAMBERLIN. 
