PHYSIOGRAPHIC PROBLEMS OF TO-DAY 645 



geography of its surface thus produced. Although man is embraced 

 in each of these categories, there are sufficient reasons for consider- 

 ing his relations to his environment separately from those of the 

 lower forms of life. 



The dependence of life on its physical environment has received 

 much attention from botanists and zoologists, and is perhaps the 

 leading thesis now claiming their attention. So important is this 

 branch of study that a name, "ecology," has been coined by which 

 to designate it. The phase of nature-study thus made prominent 

 pertains to the marvelously delicate adjustment that has been found 

 to exist between the distribution of life and the nature of the region 

 it inhabits. Among the interesting themes involved are topographic 

 relief, degree of comminution and disintegration of the surface 

 blanket of rock-waste, depth and freedom of penetration of water 

 and air into the life-sustaining film of the earth's surface, and the 

 concurrent changes in life with variations in these and other physical 

 conditions. In this most fascinating branch of study the ecologist 

 borrows freely of the physiographer, and makes payment in peat- 

 bogs, living vegetable dams in streams, organic acids serviceable 

 for rock disintegration and decay, deposits of calcium carbonate 

 and silica in lakes and about springs, vast incipient coal-beds in the 

 tundras of the far north, and numerous other ways. 



From the physiographic point of view, however, the many and 

 intricate ways in which life leads to modifications in the features of 

 the lithosphere are of more direct interest than studies in ecology. 

 Much has been accomplished in this direction, but it is evident that 

 as yet but partially explored paths leading through the borderland 

 between biology and physiography remain to be critically examined. 



In connection with the changes in progress on the earth's surface, 

 due to the influence of organic agencies, and the application of that 

 knowledge in interpreting past changes, the study of the influences 

 exerted by the lowest forms of life in both the botanical and the 

 zoological scale seems most promising to the physiographer. 



The secretion of calcium carbonate and silica by one-celled organ- 

 isms, as is well known, has led to the accumulation of vast deposits 

 like the oozes on the sea-floor, beds of diatomaceous earth, deposits 

 about hot springs, the so-called marl of fresh-water lakes, etc. A 

 review of the several ways in which such accumulations are formed, 

 and an extension of the search in various directions, give promise 

 that other and equally wonderful results flowing from the activities 

 of the lowest form of life will be discovered. The mode of deposi- 

 tion of iron, and perhaps of manganese, the generation of hydro- 

 carbons, the origin of extensive sheets of seemingly non-fossiliferous 

 limestone and dolomite, the method by which the beautiful onyx 

 marbles are laid down, film on film, the nature of the chert so 



