2/4 The American Geologist. November, i898 
Prof. Whitney in the introduction to "Some Physical Prop- 
erties of Soils," states that chemical analysis has not explained 
the relation of soils to plants or the local distribution of the 
latter ; that the gefieral distribution of these is determined by 
temperature and rain-fall, but the local distribution, by the 
relation of the soils to moisture. 
If the statements so far made are true can we not reason 
further, and say that without the operation of surface tension 
the very existence of land vegetation, or at least the greater 
part of it, would be threatened? But for capillarity would 
not rain waters escape through, or over, the soils too rapidly 
to be available? Would the film of water directly attracted 
by each grain of soil succeed in resisting evaporation, and if 
it did, how extensively would it support vegetation? Where 
would the plant food come from? And another, more funda- 
mental, question, — to what extent would the fine-grained ma- 
terials, constituting soils, accumulate, and how long would 
they rest in one place? In short would land vegetation have 
a soil permanent enough to grow in? 
From a consideration of the facts it is evident that the ex- 
istence of the former, and the permanency of the latter are 
largely inter-dependent, and that, besides this, each is directly 
dependent (the degree being the only question) on the opera- 
tion of the surface tension of water. 
If they should dry without the influence of the tension on 
the free surface of water, they would dry into incoherent "pow- 
der," "sand" or "dust," and no crust, more or less solid, w^ould 
be formed. And, on the other hand, if surface tension did not 
operate to elevate, in soils, water from below, they would dry 
after wetting in a much shorter time. 
In the former case soils would be subject to erosion to a 
vastly greater extent than they are, owing to the absence of a 
crust and the general consolidation shown to result from dry- 
ing. 
In the latter case the presence of the water obtained by 
capillarity renders the soils somewhat tough and coherent, in 
a different fashion, and so again tends to retard erosive 
agencies. 
Thus surface tension acts in two direct ways to preserve 
these materials from erosion — by the wind, the impact of rain, 
or flowing water. , 
