88 .RevieiDS — Dr. JReusch's Norwegian Researches. 



cult to determine. It is full of clalorite, accompanied by some dark 

 scaly mica. These minerals occur in the fragments as well as in the 

 ground-mass. The chloritic sparagmit is followed by a narrowband 

 of calcite-bearing gneiss, and then we come to the important zone 

 mainly composed of saussurite-gabbro and amphibolite-schist. 



(2) Zone of Saussurite-gabbro. 



The predominant rock of this zone is especially characterized by 

 the structure -known in Germany as the Riesen-flaser-struktur. 

 This structure is thus described by Credner : " An plumpe Linsen 

 Yon kornigem, massigem bis flaserigem Gabbro und flaserigem Am- 

 phibolit schmiegen sich langgestreckt linsenformige Schmitzen 

 und Lagen von diinnschiefrigem und langflaserigem Amphibol- 

 schiefer an und erzeugen so die Riesen-flaser-struktur." Credner 

 regards the Flaser-gabbro of Saxony as sedimentary and as a divisiorl 

 of his granulite formation, which he also considers sedimentary. 

 Naumann on the other hand regards both as eruptive. The author 

 is not satisfied with either of these explanations. He uses the term 

 gabbro to include true gabbro and coarsely foliated amphibolite 

 schist, because these two rocks stand in such an intimate relation to 

 each other in the Bergen peninsula and also in Saxony, that the 

 separation of one from the other is only of interest from a petro- 

 graphical point of view. 



He then describes and figures several occurrences in Saxony which, 

 illustrate the intimate relations in question, and concludes that in 

 order to account for them it is necessary to suppose that the rocks 

 became plastic, not necessarily by heat, after the felspar and horn- 

 blende had been formed. He does not agree with Credner that the 

 structures in question indicate a sedimentary origin, and states tbat 

 similar structures may be observed in the undoubtedly eruptive post- 

 Silurian syenite of Langesundsfjord.^ The constituents of the 

 saussurite-gabbro are next described. 



The saussurite is a whitish finely crystalline or compact substance 

 formed of epidote, zoisite, and here and there triclinic felspar. Tlie 

 second constituent is in many cases hornblende. Typical diallage 

 and intermediate forms between diallage and hornblende also occur. 



When considered in the light of Dr. Lehmann's more recent 

 researches, it appears probable that the hornblende is almost, if not 

 entirely, a secondary product. Evenly bedded rocks appear from 

 the author's desci'iption to be exceptional in this zone : nevertheless 

 they have been observed especially in the south-western area. The 

 bedded structure is due to variation in the size of the individual con- 



^ The development of foliation, and other structures which especially characterize 

 some of the crystalline schists in igneous rocks by combined chemical and mechanical 



'agencies is a subject of great importance. It will be discussed by Dr. Lehmann 

 in a work about to be published, entitled " Die Entstehung der altkrystallinischen 

 schiefer-gesteine," of which a short notice has already appeared in the " Annales 

 de la Societe geologique du Nord, 1883," by M. Barrels. Dr. Lehmann treats 

 especially of the Granulit formation of Saxony. He brings forward a large number 

 of facts to show that the amphibolite schists above referred to are developed from. 



. the gabbro, an eruptive rock, by combined chemical and mechanical agencies, the 

 amphibole being of course the metamorphosed representative of the diallage. 



