382 Mejjorfs and Proceedings — Geological Society of London. 



leading cross faults intersected the east-and-west Central Alpine 

 baud, and shows how the coalescence of these cross faults with 

 E.N.E.-W.S.W. faults on the north side and W.N.W.-E.S.E. faults 

 on the south side defined two leading fault curves, the one passing 

 through the Engadine and continuing in the Dalmatian Alps, the 

 other passing through the Western Alps and continuing in the 

 Apennines. These strike curves are essentially peripheral to the 

 western side of the Hungarian Basin. 



The cross segment comprising the Rhine-Ticino district between 

 the Western Alps and the Engadine is, according to the authoress's 

 'interpretation, anticlinal in character, segments having been down- 

 thrown from it both towards the west and towards the east, and 

 overthrust masses having crept eastward and south-eastward from 

 the Western Alps, and westward from the Engadine. 



The authoress then discusses the relation of the French Jura 

 Mountains to the Alpine System, pointing out that the Swiss-French 

 Plain flanking the Western Alps presents the same essential features 

 of structure, in relation to the Western Alps on its east side and the 

 French Jura Mountains on its west, as those that she has elucidated 

 for the Ehine-Ticino cross segment. She consequently interprets 

 the strike-curve round the west formed by the Jura Mountains and 

 the ranges of Dauphine as the outermost peripheral plicational 

 system in the Alps, showing that the whole region between the 

 Hungarian Basin and the ancient mountain groups of Central France 

 has been under the influence of the westward thrust. 



The general principle of structure treated of above — namely, the 

 sagging of crust-blocks by means of normal faults towards bands or 

 localities of crust- weakness or subsidence, and the reverse or over- 

 thrust movements which may take place from within these bands or 

 localities — is that which the authoress demonstrated in the Dolomite 

 Massives in 1893, and has ever since advocated as a leading principle 

 in the interpretation of Alpine structures, the important considera- 

 tion being that where, as in the Alps, the principle is applicable in 

 relation to two intersecting axes of deformation, the phenomena pro- 

 duced must necessarily be of the nature of ' interference phenomena.' 



A leading feature of the paper is the evidence that it affords of 

 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 dis- 

 placement; 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.N.E. direction, and on the south side 

 towards some N.W.-S.E. or W.N.W.-E.S.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. 



