506 



NA TURE 



{Sept. 20, 1888 



determine more precisely their mutual relations. It is here, 

 again, gentlemen, that the knowledge that you bring from many 

 parts of the world may aid us in throwing light on this difficult 

 subject. 



Amon^ the other questions which preceding Congresses have 

 not decided, are : — 



(1) The relation between the Carboniferous and the Permian. 



(2) Between the Rhsetic and the Jurassic. 



(3) Between the Tertiary and the Quaternary. 



When there is m interruption in the continuity of the strata, 

 and no discordant stratification, the systems pass one into 

 another without apparent break, like the colours of the solar 

 spectrum ; but, as you all know, if one link is wanting, the chain 

 is broken, and the line of separation of the disunited beds be- 

 comes sharply defined. If, for example, the Caradoc should be 

 absent in the Cambrian-Silurian, or the Pliocene should be want- 

 ing in the Tertiary, there would be between these systems a 

 break which would give the necessary relief to the superimposed 

 strata. The primary colours of the spectrum are not less dis- 

 tinctive because they pass one into the other with intermediate 

 shades ; nor does it follow that, because there are passage-beds, 

 the systems form one whole. There must be, somewhere, 

 passage-beds between them, as there are between the colours. 



Apart from these international questions, the Berlin Congress 

 was occupied with several special memoirs, but we are yet with- 

 out particulars, and besides, whatever may be their interest, 

 they concern us less for the moment than international questions. 

 Among others of the latter, a great palscontological project has 

 been mooted, and the Congress has appointed a Commission of 

 distinguished palaeontologists to co-operate towards its realiza- 

 tion. A work is proposed, on the plan of the " Enumerator et 

 Nomenclator" of Brown, and of the "Prodrome" of Alcide 

 d'Orbigny ; but such is the progress that palaeontology has made, 

 that at present, for the enumeration of all the known fossils, of 

 animals as well as plants, a publication of some fifteen large 

 volumes would be required. A work of this kind will make a 

 handsome pendant to the large polyglot dictionary of geological 

 terms, projected at Bologna. 



Such, gentlemen, are some of the questions and subjects that 

 you have to consider. You have to revise and to settle, when 

 possible, questions already discussed, and also to discuss new 

 problems. Among the latter there is especially the funda- 

 mental question of the crystalline schists — a subject remarkable 

 for the great progress that it ha~ made during the last few years, 

 and the entirely new aspect that it is assuming ; for it is evident 

 at present that it is not only a chemical question of meta- 

 morphism by heat, but that it is a subject which entails ques- 

 tions of weight, pressure, and motion, which necessitate a wide 

 co-operation, and the combined efforts of the physicist, the 

 chemist, the petrologist, and the stratigraphist. 



Although the greater number of the subjects considered by 

 the Congress are eminently practical and positive, they also in- 

 clude theoretical questions of the highest interest. The classi- 

 fication of the strata and their synchronism over great areas, 

 which you have to determine, rest both upon stratigraphy and 

 upon palaeontology. In order to adjust their precise relation, 

 you have to note the identities as well as the differences of fossil 

 species, and to know if the order of the beds in distant countries 

 follows a synchronous order or is only homotaxial. In the one 

 case, we can hardly expect to find similar species ; in the other, 

 the identity of species may be taken as a proof to the contrary, 

 unless it may be supposed, as Edward Forbes thought, that 

 species have had more than one centre of origin. 



To solve these problems you have to trace the dawn of life, 

 the appearance, the duration, and the disappearance of species, 

 and the source from which they come. Are we to believe in 

 the evolution of species, or are we to regard them as shoots of 

 short duration, and the genera or families as the branches or 

 permanent trunks? If I have ventured to touch upon these 

 problems of fact and theory, it is not to express an opinion, but 

 merely to point out how vast the field is, and how many 

 fellow-labourers and how long is the time required to make all 

 the necessary studies. 



It must not be thought that when the fundamental questions 

 of fact are determined the work of the Congress approaches 

 completion. General agreement on these international questions 

 will only smooth the way, and one can foresee in the cosmopolitan 

 problems of theory already considered, and in many others that 

 cannot fail to arise, what will occupy in a long and useful future 

 all the efforts of this International Congress. 



ON THE CONSTITUTION AND STRUCTURE 

 OF THE CRYSTALLINE SCHISTS OF THE 

 WESTERN ALPS} 



TEN years have elapsed since Prof. Lory first formulated his 

 views on the crystalline schists of the Western Alps, at the 

 Congres International de Geologie held in Paris in 1878. These 

 he subsequently developed at the Reanion de la Societe Geo- 

 logique de France at Grenoble in 1881. Since then further 

 work in the field has strikingly confirmed these views, and Frof. 

 Lory has taken aivantage of the opportunity given by the 

 invitation of the Organizing Committee of the Geological 

 Congress to summarize briefly the more important facts, derived 

 from the study of the Western Alps, that have a direct bearing 

 on the general question of the crystalline schists. 



The crystalline schists appear in the Alps in massifs of greater 

 or less extent, protruding through the sedimentary formations. 

 These massifs are distributed in two principal zones, arched in 

 agreement with the general curvature of the Alps. These the 

 author proposes to designate the first Alpine '.one, or Mont- Blanc 

 zone, and the fourth Alpine zone, or Monte-Rosa zone. The inter- 

 mediate zones (se ond and third Alpine zones) are of less im- 

 portance, the outcrops being rare and of small extent. As they 

 resemble the fourth zone in their principal characters, they are 

 treated in its connection. 



(1) The fourth Alpine zone, or zone of Monte- Rosa, is by far the 

 largest. In it the crystalline schists are exposed over the greater 

 part of the Italian slopes, and skirt the plain from Cuneo to 

 Lake Maggiore. Their stratification is often nearly horizontal, 

 and always conformable with the sedimentary formations (Trias 

 or Jura) resting upon them. 



It is subsequent to the deposition of these Secondary rocks 

 and, very probably, even much later— in Tertiary times — that 

 this part of the Alps has been fashioned into mountains by 

 the lateral pressure resulting from the gradual subsidence of the 

 vast regions represented by the plains of Italy and the basin of 

 the Adriatic. The result of these i oportant dynamic processes 

 was the formation of a complex of great folds, which are often 

 much complicated by faulting. 



The succession of the different groups of crystalline schists in 

 this zone is conformable to the order indicated, long since, by 

 Cordier. It is necessary to point out, however, that this upper 

 group — that of the taleites (talc-schists) — contains talc only as 

 an accessory constituent ; the unctuous (talcoid) aspect being due, 

 in reality, to the presence of certain indistinctly cleavable and 

 fibrous varieties of mica, especially sericite. These schists may 

 be termed sericite-schists or, abbreviated, serischists. In the 

 purer varieties they are of a nacreous white or clear gray colour ; 

 but by the addition of chlorite they assume greenish tints and pass 

 into chloritic and quartzose schists — the chloritoschists which 

 attain so great a development in the whole of the Western Alps. 

 Alternating frequently with these rocks are hornblendic schists, 

 of which the development is very variable. In certain parts of 

 the Italian Alps, however, especially between Ivrea and Domo 

 d'Ossola, they become predominant. 



This upper division of the crystalline schists is characterized 

 by a more or less pronounced green tint, due to the presence of 

 chlorite or hornblende, which recalls the name pietre zvnli, 

 given to these and other schists by Gastaldi and several other 

 Italian geologists. 



Below the chloritic and hornblendic schists occurs a large 

 series of mica-schists, with which are intercalated, in conform- 

 able bedding, cipolin-limestones (ealeaires cipolins), granular 

 dolomites, and pure saccharoidal limestones, alternating with 

 mica-schists and evidently forming part of the same formation. 



The mica-schists become charged with felspar and pass thus 

 into gneiss, with which they alternate. Black and white micas 

 are a-sociated in these rocks. In proportion as the series is 

 descended, orthoclase becomes more abundant, and the gneisses 

 predominate with a foliation which decreases until they pass 

 into granitoid gneiss, in which the foliation disappears, but 

 the broader features of stratification remain visible. This is 

 well shown in the section of the Simplon massif, where the 

 gorges of the Diveria are hollowed out, to a depth of 700 

 metres, in the horizontal beds of the granitoid gneiss known as 

 the gneiss of Antigorio. 



1 "Sur la Constitution et la Structure des Massifs de Sohistes Cristallins 

 des Alpes Occidentales," par M le Professeur Ch. Lory. " Etudes sur les 

 Schistes Cristallins." London, 1888. (Abstracted from the French by Dr. 

 F. H. Hatch.) 



