Sept. 20, 1888] 



NA TURE 



50; 



Prof. Lory does not recognize in the Monte-Rosa zone any beds 

 belonging to the Carboniferous ; and he believes that the crystal- 

 line chistsof this part of the Alps have been exposed during 

 the whole of Palaeozoic times, without having been disturbed 

 from their primitive horizontal position. They have gradually 

 subsided during the Triassic period. The lower stages of this 

 formation are not much developed in this zone ; but the upper 

 stage, represented by the schistes lustres, have acquired an 

 enormous thickness. 



These Triassic beds are characterized by a remarkably crystal- 

 line texture. The limestones and dolomites which form the 

 middle stage are granular and saccharoidal, and inclose authigenic 

 crystals of albite. The schistes lustres are composed in great 

 part of crystallized minerals (quartz, mica, tourmaline, garnets, 

 &C.), which are also certainly authigenic. This crystalline 

 condition is uniform and constant, and independent of all 

 dislocations and c ntortions which the beds have subsequently 

 undergone. 



The crystalline character of the sedimentary formations may 

 be of assistance in understanding the origin of the crystalline 

 schists. The foliation is generally parallel to stratification, the 

 latter being always very distinct. Characters so uniform cannot 

 be explained by the phenomena of slaty cleavage and crystalliza- 

 tion under the influence of local mechanical actions. It is rather 

 a general, universal, and original crystallization of the primitive 

 rocks, which took place anterior to the deposit of all sedimentarv 

 formations. 



The most important element of Prof. Lory's third zone are 

 anthracitic sandstones. These sandstones belong to the Upper 

 Coal-measures (houiller supirieur). The boundary between them 

 and the crystalline schists is usually marked by a fault. But 

 sometimes, as at the bridge of St. Andre, near the railway 

 station at Modane, the latter appear under the sandstones, and 

 then the foliation of the crystalline schists is conformable with 

 the bedding of the Carboniferous sandstones. At this and other 

 localities there occur in the lower portions of these sandstones 

 conglomerates formed of slightly rolled fragments of crystalline 

 schists, identical with those which crop out in the neighbourhood. 

 It is therefore evident that the foliation and cry. tallization of the 

 crystalline schists must be earlier than the Carboniferous period. 

 Conglomerates, composed of fragments of the most diversified 

 rocks from th,e crystalline schists, occur in the Upper Trias, in the 

 Lias {Col du Gold), and in the Nummulitic Eocene {massif des 

 End mbres). Each of these conglomerates contains fragments of 

 all the preceding formations. Since these rolled pebbles have 

 the characteristic structure, crystalline or foliated, of the rocks 

 they are derived from, and since the foliation of the pebbles 

 has no uniform direction in the conglomerates, it follows that 

 the foliated or crystalline texture of the rocks of these various 

 formations is, each for each, of earlier origin than the deposition 

 of that which overlies it, and absolutely independent of the power- 

 ful mechanical actions which only fashioned these formations 

 into mountains subsequently to the Eocene period. 



Again, all the formations, from the Trias to the Eocene, 

 contain microscopic crystals of silicates (felspars, mica, quartz, 

 tourmaline), which ate of contemporaneous origin with the rocks 

 containing them, and do not, therefore, owe their existence to 

 any of the dynamic processes which have subsequently acted 

 upon this part of the Alps. 



Since these silicates, which are identical with, or very 

 analogous to, those of the crystalline schists, were formed in 

 the Secondary and Tertiary deposits independently of all 

 eruptive actions or special emanations, and anteriorly to all 

 dynamic processes, it is unnecessary for the explanation of 'he 

 origin of the primitive crystalline schist., to assume physical 

 conditions absolutely different from those of the Secondary or 

 Tertiary periods. 



In the remote epoch in which these schists were formed there 

 were no terrestrial features, and consequently no detiital forma- 

 tions. The existence of organisms in a universal ocean, warmer 

 and more heavily charged with saline matters than actual seas, was 

 not yet possible ; and there resulted combinations of crystallized 

 minerals, the formation of which in later times became more 

 local and restricted. But even as late as Tertiary times we still 

 find traces of analogous reactions in the deposits of those remark- 

 able fiords of the Pocene period which extend over a part of the 

 actual site of our Alpine chains. 



(2) Prof. Lory's first Alpine zone, or Mont-Blanc zone, com- 

 prises, in Switzerland, the masdfs of the Bernese Alps and of St. 

 Gothard ; in Savoy, those of the Aiguilles Rouges and of Mont- 

 Blanc ; the chain of Belledonne ; the small massif of Rocheray, 



near St.-Tean-deMaurienne ; the massif at Rousses, in Oisans ; 

 the massif 'of Pelvoux, between Drac and Durance ; finally, the 

 massif of the Maritimes Alps, between the Col de l'Argentiere 

 and the Col de Tende. 



The characteristic feature common to all these massifs consists 

 in the crystalline schists composing them being nearly always 

 highly inclined or almost vertical. They do not appear to pre- 

 sent the regular structure — the great anticlinal folds of the Monte- 

 This indicates that fat Mont- Blanc zone is really the 

 ancient part of the orogenic system of the Alps, and that i's 

 structure has resulted from the dislocations of different epochs. 



Anthracitic sandstones occur also in this zone, but they are 

 less developed and less continuous than in the third zone, and, 

 as indicated by their plant remains, are of more recent date, being 

 intermediate between the Coal-measures of Rive-de-Gier and 

 those of Saint- Etienne. 



On the western slope of this zone traces of dislocations, 

 anteiior to the deposition of these Carboniferous sandstones, can 

 be recognized. They are indicated by clear unconformities at 

 various p. ints in the Mure. basin and other places. But on the 

 eastern slope of the same zone the Carboniferous sandstones and 

 the crystalline schists are generally conformable. 



These Carboniferous sandstones of the_//V.v/ zone, like those of 

 the third, are accompanied by conglomerates containing numerous 

 fragments of foliated crystalline schists, of which the petro- 

 g aphical characters are identical with those of the underlying 

 crystalline rocks. These conglomerates are well known on both 

 western and eastern slopes (poudingues of Yalorsine, Grandes- 

 Rousses, &C.) Since the Carboniferous sandstone on the eastern 

 slope is conformable with the crystalline schists, the existence of 

 large fiagments of the schists in these conglomerates, clearly 

 demonstrates that their foliation is anterior to all dislocations 

 which have affected the massif. It was after the deposition of 

 the anthracitic sandstone, between the Carboniferous and Triassic 

 periods, that the principal dislocations took place, which have 

 upheaved and contorted the crystalline schists and the anthracitic 

 sandstones of the first zone. Wherever the Triassic beds appear 

 nearly horizontal they rest, in conformable stratification, on the 

 upturned edges of tne older formations, whether anthracitic 

 sandstones or crystalline schists. 



The horizontal position of numerous shreds of Secondary rocks 

 to be found at very variable heights indicates the character of the 

 dislocations which have taken place at more recent periods in this 

 part of the Alps. The ancient formations, already upheaved and 

 contorted before the deposition of the Trias, have behaved like 

 rigid masses, and have not lent themselves to the newer folding. 

 They have been traversed by faults ; and displacements have 

 taken place along the planes of fracture, while at the same time 

 following the divisional planes of stratification. The Secondary 

 rocks, on the other hand, have behaved like flexible, and even, 

 when argillaceous, like plastic bodies. They have only been com- 

 pletely fractured by the more important major faults ; everywhere 

 they have moulded themselves by multiplex folding to the new 

 forms of their dislocated base. This flexible covering has slipped 

 into the depressions formed by the subsidence, due to dislocation, 

 of certain parts of its base. In this way the Secondary rocks pre- 

 sent themselves on the Hanks of the Alpine valleys in beds which 

 are inclined and contorted in repeated folds, contrasting thus with 

 the uniform curvature of the ancient rocks. 



The powerful mechanical actions resulting from these disloca- 

 tions of the first Alpine zone have often superinduced, in the 

 argillaceous limestones of the Lias, phenomena of "stretching,"' 

 lamination, and, above all, a slaty cleavage in a direction different 

 from that of stratification. As to the crystalline schists, of which 

 the plication took place at the end of the Carboniferous aiul 

 before the Triassic period, the more recent dislocations have 

 destroyed the regularity of their anticlinal and synclinal folds. 

 Along the axes of the anticlinal ruptures, or following the bands 

 of mica-schists— that part of the crystalline schists which offers 

 least resistance — occurred the subsidences which have given rise 

 to the actual Alpine valleys ; it is following these directions, and 

 nearly always following the old synclinal folds, that the ancient 

 rocks have been cut up into massifs, separated by the bands of 

 depression, where the Secondary rocks, adapting themselves to 

 the new forms assumed by their base, have descended while 

 undergoing plication ; and their beds, highly inclined and often 

 curiously folded, clothe the lateral walls of these depressions. 

 The valley of Chamonix and l'Allee Blanche, the Combe d'Olle, 

 the lower valley of the same stream, at Allemont, and that of 

 Bourg-d'OisaDS, are examples of this type of longitudinal Alpine 

 valleys of the Mont- Blanc zone. 



