﻿Interference-Phenomena in the Alps. 531 



differential rates of movement in different parts of a thrust-mass, or 

 fault-block undergoing horizontal displacement, both in respect of 

 the laterally-adjacent parts of a thrust-mass and also of the subjacent 

 layers. The writer's maps and sections show that the actual de- 

 formations which characterize a thrust-mass have a different direction 

 of strike on either side of an axial band of maximum horizontal 

 displacement ; for example, if the horizontal movement of a thrust- 

 mass is westward, the deformational phenomena (faults, folds, etc.) in 

 the western front of the thrust-mass curve on the north side towards 

 some S.W.-N.E. or W.S.W.-E.X.E. direction, and on the south side 

 towards some N.W.-S.E. orW.N.W.-ES.E. direction. The authoress 

 interprets these observations on the basis of the deflection of the 

 general movement of the thrust-mass by the strains set up between 

 the axial region of maximum horizontal displacement and the lateral 

 regions where from any cause the horizontal displacement is less. 



Another feature which may be mentioned is her description 

 of several examples in the Dolomites where there had apparently 

 been a local reversal of the regional westward movement, and her 

 reference to the familiar examples of eastward overthrusts in the 

 Judicarian district, and on the eastern and south-eastern front of 

 the grander mountain-massives of the Swiss and French-Italian 

 Alps. "While each individual case demands special examination, she 

 indicates an explanation that satisfies certain cases which she has 

 examined. At localities where the base of the thrust-mass is open 

 to inflows of igneous rock, the igneous material may ascend and be 

 carried onward with the gliding mass, undergoing consolidation 

 during the movement, and inducing contact-changes in neigh- 

 bouring rock-material. After consolidation of such igneous inflows, 

 they present resisting bodies within the thrust-mass, which, in the 

 same way as any massive developments of hard sedimentary material, 

 impede the advance of rock-material in the same direction as before, 

 and thus cause local deflections. The tendency is for the material 

 of the thrust-mass to be strongly plicated and faulted as it is driven 

 against any such resisting body, widening out in a direction roughly 

 parallel with the resisting mass, and piling up the material in front 

 to such an extent that local reversal of the direction of overlapping 

 is produced. 



2. ' The Influence of Pressure and Porosity on the Motion of 

 Sub-Surface Water.' Bv "William Ealph Baldwin-Wiseman, M.Sc, 

 AssocM.Inst.CE., E.G.S. 



The author commences the paper with a brief historical summary 

 of the researches which have been conducted since 1830 on the 

 motion and behaviour of underground water, more especially dealing 

 with the question of sub-surface flow and the delimitation of cones 

 of depletion. 



In the second part of the paper, in discussing the influence of the 

 porosity of a rock on the rate of flow of water through it, he de- 

 scribes in detail the variations in porosity which may occur in 



