15 



of time, in direct ratio to the length and in inverse ratio to the 

 fourth power of the radius of the channel. 



How considerable this resistance is in relatively porous rock, as 

 e.g. the gres bigarré, is shown by A. Davukkk, in a note on his 

 experiments about capillary attraction. 



Daubreï^ draws attention to the fact that a thin disc of sandstone 

 2cm. thick, whicli completely shuts off a basin partly tilled with 

 water, is able to prevent water-vapour to escape (through the body 

 of the rock) even lohen the vapour has acquired a tension of several 

 afinosj^heres. 



When now we take into consideration that the ratio of the dia- 

 meters of capillary channels in sands and those in clays may be 

 as from lODO to 1, we shall be able to form an idea of the excessive 

 resistances prevailiing in finegrained sediments. (In inverse ratio to 

 the fourth power of the radius). 



Where moreover, the researches in folded areas have shown that 

 the magnitudes of such fine-grained sedimentary (argiliceous-, imper- 

 meable-) strata may amount to hundreds and even thousands of meters 

 in thickness, covering the Iota! extent of the G.S., it does not seem 

 unwarranted to pose the possil>i!ity of such impermeable strata 

 preventing the water (vapour) occupying the capillary channels of the 

 sedimentary deposits, from being expelled therefrom by the intluence 

 of the high temperatures and tensions engendered in those strata, 

 on their way down to the zone of liquefaction. 



This contribution purposes to point out a direction in which it 

 might be considered possible to look for a satisfactory solution of 

 the problem of the origin and the mechanism of volcanism. 



(In the paper now in course of preparation, in collaboration with 

 others, and which we hope to be able to publish in the Journal of 

 Geology (Chicago, U.S.A.) before long, we intend to calculate the 

 values of vapour-tensions at temperatures of 1000^ — 1200° C. in 

 connection with the quantity of water supposed to be occluded in 

 the sedimentary strata and their respective volumes ; further to 

 approximate the frictional resistance in sedimentary strata built u|t 

 tVom clay and (or) sand, in order to ap[)roximate how thick a body 

 of clay or sand should be, so that the frictional resistance (in its 

 capillary channels) be sufficient to prevent the water occluded in 

 the underlying sedimentary nuisses, to be expelled therefrom). 



LITERATURE. 



1. A. Daubrée. Etudes synlhetiques cle Geologie expérlmentale. Paris 1879, 



2. T. V. WoT-FF. Der Vulkanismus. Berlin 1914. 



