+Volcanic Gases+ 617 Differences in gas action, 617. Spasmodic action, 618. Kinds of gases, 618. Residual gases in volcanic rock, 619. The source of the gases, 621. +The Cause of Vulcanism+ 623 I. _On the Assumption that the Lavas are Original_ 623 Lava outflows from a molten interior, 624. Lavas assigned to molten reservoirs, 624. II. _On the Assumption that the Lavas are Secondary_ 625 Lavas assigned to the reaction of water and air penetrating to hot rocks, 625. Lavas assigned to relief of pressure, 627. Lavas assigned to melting by crushing, 628. Lavas assigned to melting by depression, 629. Vulcanism assigned to the outflow of deep-seated heat, 629. _Modes of Reaching the Surface_ 631 _Additional Considerations Relative to the Gases_ 633 _Thermal Considerations_ 635 CHAPTER XI. THE GEOLOGIC FUNCTIONS OF LIFE. I. +The Distinctive Features of Organic Processes+ 638 _The Chemical Work of Life_ 638 Life material chiefly atmospheric, 638. The non-atmospheric factors, 639. (1) _Changes in the composition of the atmosphere_ 639 The consumption and restoration of carbon dioxide, 640. The freezing and consumption of oxygen, 640. The organic residue, 640. The meaning of the organic residue, 641. The more inert factor, 642. Probable fluctuations of atmospheric composition, 642. The climatic effects of organic action, 643. (2) _Aid and hindrance to inorganic action_ 644 The promotion of disintegration, 644. Protection against erosion, 644. The influence of land vegetation on the character of the sediments, 645. (3) _Distinctive deposits_ 646 Organic rocks, 646. Inorganic rocks due to life, 646. _Fossils_ 646 The general order of life succession determined by stratigraphy, 647. Fossils as means of correlation, 647. _Special Modes of Aggregation and of Movement_ 648 _The Mental Element_ 649 (1) The material effects of the mental element, 649. Human modification of the animal and vegetal kingdoms, 650. (2) The psychological factors as such, 651.