RevieiDS — Geology of Central Norway. 327 



sparagmite, and which he believes to be the oldest part of that 

 formation. 



Passing to the tributary valley of the River Jora, the author deals 

 with a rock, which, though resembling sparagmite, rests upon and 

 not under, the Silurian, and he names it the Younger Sparagmite. 

 He believes it to be of Devonian age. It is closely associated with 

 the post-Silurian eruptive rocks of the Jotunheim Mountains. 



The fourth part of the work deals with Valdres, Hemsedal, and 

 Laerdal, and the author ti'aces the Younger Sparagmite to the Sogne 

 Fjord, and soixth-west into the district around Vossevangen. The 

 rocks included in the Younger Sparagmite Formation are a part of 

 those grouped together by Kjerulf ^ under the general title Hoifjelds 

 kvartsen. 



Brogger speaks of the group as the Younger Gneiss Formation, and 

 has described it in his valuable memoir on the Hardanger vidda.^ 

 He points out that in places it bears a great resemblance to 

 the Archgean Gneiss, but, like Kjerulf, he treats the succession as 

 normal, and the Younger Gneiss as of later date than the Silurian 

 schists upon which it rests. 



In the present work Mr. Bjorlykke describes how various authors, 

 himself included, have been led to suggest that some part, at least, 

 of this younger gneiss may be overthrust masses of the Arch^an. 

 Professor A. E. Tornebohm has gone much further, and has brought 

 forward a series of overthrusts on a gigantic scale in explanation of 

 the structure of the Scandinavian mountains. 



Mr. Bjorlykke's recent work in the field leads him to think that the 

 theory of overthrusting has been carried much too far, and he doubts 

 whether the evidence goes further than to show quite local pushing 

 of strata over one another. He accordingly reverts to the opinion of 

 Kjerulf and Brogger, that the succession is on the whole normal, and 

 the Younger Gneiss group newer than the Silurian schists. He 

 divides that group into two parts. The first is the Younger 

 Sparagmite Formation, of which we have already spoken, and in the 

 other he places the more gneiss-like rocks, suggesting that they are 

 more or less metamorphosed igneous rocks connected with the great 

 mass of post-Silurian eruptives which are largely developed around 

 the head of the Sogne Fjord and in the Jotunheim Mountains. 



The author explains that Norway is affected by two systems of 

 folding. The first, which he terms the " Mountain-chain " system, 

 runs N.N.E. and S.S.W., whilst the other, which he terms the 

 "Strike-system," runs W.N. W. and E.S.E. 



The memoir is accompanied by a sketch-map geologically coloured, 

 and numerous maps and photographs are inserted in the text. 



In the Supplement, Professor Lapwortli describes and figures a 

 series of Graptolites collected by Mr. Bjorlykke in Gudbrandsdal. 



Horace W. Monckton. 



1 Th. Kjerulf, "Udsigt over det sydlige Norges geologi," Christiania, 1879, p. 164. 

 - " Lagiolgen paa Hardanger ndda iS^orges Geologiske undersogelse," No. 11, 1893. 



