REVIEWS. 643 



Professor Bertrand has extended the work to the westward, and 

 brings together in two papers the results of* his four years' work in 

 the French Alps. The first paper describes the structure and meta- 

 morphism, while the second is devoted to a discussion of the lustrous 

 schists. 



The structure is that of the fan with the folds on the west dipping 

 toward France and on the east toward Italy. In the neighborhood of 

 St. Maurice and Briancon, the axis of the fan is formed of Carbonif- 

 erous rocks; while farther south, it is formed of Eocene layers inclin- 

 ing in the same way. While the Carboniferous zone on its western 

 border forms a curve regular and parallel to the axis of the chain, the 

 interior folds are remarkable for their irregularities. The cause of 

 this difference is the presence of elongated lenses occurring in the 

 synclines and anticlines. Such an arrangement resembles the augen 

 (amygdaloidal) gneiss, so the name amygdaloidal (augen) structure is 

 proposed. To illustrate the importance of these lenses, Mt. Blanc is 

 found to be one large lens or augen rising from a synclinal area. 



All this region of the Alps during Carboniferous, Triassic, and 

 probably Jurassic time has been the seat of continuous sedimentation. 

 The later movements have restored to light these ancient sediments 

 and have shown the depths to which they have been buried. 



While in one case the lustrous schists seemed to be of Palaeozoic 

 age, in all other places they are better interpreted as Triassic. The 

 very great development of green rocks of apparently Triassic age 

 seemed exceptional, but they were found in other places associated 

 with fossils. The author regards the Hudson river group in the 

 United States, as described by Walcott, as the first instance comparable 

 to these lustrous schists. Similar bodies of schistose rocks as a 

 facies of fossiliferous beds occur in Scandinavia and the Pyrenees. It 

 is, then, a general fact that on the site of the important mountain chains, 

 before their formation was complete, there was active sedimentation 

 with a schistose facies limited to the synclines and usually of basic 

 rocks. In this region there was a rapid filling up of the geosynclines 

 in the flysch periods. The Triassic flysch was formed at the centre of 

 the chain before the first submergence. The Eocene flysch was depos- 

 ited on the border of the chain already emerged, and this was followed 

 by active denudation which resulted in a recent rupture of the equilib- 

 rium. That the age of these lustrous schists is Triassic there is but 

 little doubt, a conclusion which agrees with the observations of Lory. 



G. Perry Grimsley. 



