646 PHYSIOGRAPHY 



abundant in many terranes and so conspicuous in the surface waste 

 of extensive regions, and other equally important deposits which 

 exert a profound and frequently controlling influence on topographic 

 forms, seemingly demand study with the hypothesis in mind that 

 they owe their origin to the vital action of low forms of plants or 

 animals. Not only the concentration of mineral matter by one-celled 

 organisms, but the part played by similar organisms in the com- 

 prehensive processes of denudation, also invites renewed attention. 

 Many of the organisms in question do not secrete hard parts, and 

 hence are incapable of directly aiding in the concentration of inor- 

 ganic solids on the surface of the lithosphere. If not assisting in the 

 building of physiographic structures, the suspicion is warrantable 

 that they are engaged in sapping their foundations. The wide dis- 

 tribution of one-celled organisms, and, indeed, as one may say, 

 their omnipresence on the earth's surface, and their seeming in- 

 dependence, as a class, to differences in temperature, light, and 

 humidity, enable them to exert an unseen and silent influence, not 

 suspected until some cumulative and conspicuous result is reached. 

 The importance of bacteria in promoting decay, and in consequence 

 the formation of acids which take a leading part in the solution 

 and redeposition of mineral substances, the role played by certain 

 legions of the invisible hosts in secreting nitrogen from the air and 

 thus aiding vegetable growth, and perhaps to be held accountable 

 also for the concentration of nitrates in cavern earths, the part 

 others play in fermentation, and the diseases produced in plants 

 and animals by both bacteria and protozoa, render it evident that an 

 energy of primary importance to the physiographer is furnished by 

 these the lowest of living forms. Physiographers were given a new 

 point of view when Darwin explained the part played by the hum- 

 ble earthworms in modifying the earth's surface. As it seems, still 

 other advances in our knowledge of the changes in progress in the 

 vast laboratory in which we live may be gained by studying the 

 ways in which organisms far lower in the scale of organization than 

 the earthworms are supplying material for the building of mountains 

 or assisting in the leveling of plains. 



In brief, a review of the interrelations of physiography and life 

 shows that from the lofty snow-fields reddened by Protococcus, to 

 the bottom of the ocean, the surface of the lithosphere is nearly 

 everywhere enveloped in a film teeming with life. In part the vital 

 forces at work are reconcentrating material and adding to the solid 

 framework of the globe, and in part, but less obviously, aiding in 

 rock decay and disintegration. Throughout this vast, complex 

 cycle of changes new physiographic features are appearing, others 

 disappearing, and one and all, to a greater or less degree, are under- 



