268 The Ainerican Geologist. Novembor, i898 
from a geological point of view, causing the penetration of 
water, upwards or downwards, or in any direction, into the 
mineral and rock constituents of the earth's crust, which in the 
main have a sufficient attraction for water to produce capillary 
phenomena. But under certain conditions the attraction is 
wanting and the directly opposite capillary effects are pro- 
duced. 
The principles of the circulation of water through inco- 
herent materials, especially soils, have been comprehensively 
discussed by Prof. Milton Whitney, in a paper entitled "Physi- 
cal Properties of Soils in their Relation to Moisture and Crop 
Distribution," and in other publications.* 
Little if anything is added here to his observations con- 
cerning the movement of water, through soils. Prof. Whit- 
ney, however, applies these principles only to the agricultural 
question of crops. They may also be considered from a more 
general point of view and in connection with other phenomena 
of surface tension of water, i. e. with reference to the relation 
of moisture in incoherent materials, and the phenomena of 
shrinkage on drying, to land vegetation as a whole, and to 
erosion. The broad questions may be asked : How far is land 
vegetation dependent on capillary waters? To what extent is 
the presence of soil-mantles dependent upon the tension on 
the free surface of water acting in capillary tubes? 
We know that owing to surface tension a movement of 
water takes place not only in the more or less incoherent ma- 
terials, but in the solid rocks themselves, and in minerals along 
cleavage planes, or wherever a rift or crevice appears, to give 
play to the necessary forces: Also, that on drying the inco- 
herent materials become more or less hard and consolidated. 
In studying these phenomena we observe, essentially, luetness 
of the material, and the continuanee of this condition, in case 
of loss by evaporation on any surface, as long as water-supply 
endures; also that the water is present in minute colunms or 
sheets, and that a lateral imvard pull exists, on the walls of 
the rock, varying with the mass of the water suspended in each 
*In order to avoid confusion of ideas it is necessary at the 
start to conceive these materials in a condition unaffected by t/ie 
surface tension of water, i. e., in a dry incoherent state, as if re- 
moved from water and dried, particle by particle, or ground or pro- 
duced originally in a dry atmosphere. 
