Vol. 50.] GNEISSES IN THE C0TTIAN SEQUENCE. 271 



very close to it. We may, therefore, conclude that the gneiss is 

 later than the earlier basic series. Eat, until it can be determined 

 at what period in the Palaeozoic era that series was intruded, this line 

 of argument only confirms the previous conclusions without render- 

 ing them more precise. 



For a more definite determination of the age of the Waldensian 

 gneisses reliance must be placed on the indirect evidence afforded 

 by a study of the main dislocations of the district. It is now 

 generally admitted that the mountains in this part of the Alps have 

 been formed by elevations at very different epochs, from the Carbo- 

 niferous (or, according to Prof. Sacco, 1 from the pre-Cambrian) to 

 the Pliocene. The evidence for, and the influence of, the different 

 movements, have been recently discussed by Kilian, 2 Haug, 3 and 

 Diener. 4 The pre-Permian movements appear to have been un- 

 important in this district, as Diener has pointed out, though 

 Zaccagna lays much stress upon them. 



The main earth-movements of the Cottians may be divided into 

 six groups : — 



1. The east-and-west fold of the Northern Cottians, which has 

 caused the anticlinal separating the gneiss of the Paradiso from 

 that of the Eastern Cottians. 



2. The north-and-south faults to which are due the valleys of 

 Turras, and the uppermost part of the Dora Biparia. 



3. The east-and-west compression to which is due the narrow 

 north-and-south chain from Brie Bouchet to the Monviso. 



4. A series of powerful thrusts from the west, which has pushed 

 the Trias on to the calc-schists — -as in the north-eastern spur of 

 Monte Chaberton and in the Roc del Boucher, and has contorted 

 the dolomites to the north of Bocca Bianca. 



5. An enormous gabbro-intrusion (possibly laccolitic) which forms 

 the Punta del Lagho, Monte Tre Denti, Monte Bobinet, and Monte 

 delle Plate, which now occupies the centre of a great circular 

 amphitheatre, 2| miles in diameter, formed of the schists of Bocca 

 Bossa, Bocca Vergia, Bocca del Mortai, and doubtless also the Costa 

 di Plantin and Costa Ciarmagranda. 



6. The intrusion of the Waldensian gneisses. 



1 F. Sacco, ' La Geo-tectonique de la Haute Italie occidentale,' Bull. Soc. 

 Beige Geol. Pal. vol. iv. (1890) Mem. p. 28. 



2 W. Kilian, ' Notes sur l'Histoire et la Structure geologique des Chaines 

 alpines de la Maurienne, du Brian (jonnais et des Regions adjacentes,' Bull. Soc. 

 geol. France, ser. 3, vol. xix. (1891) pp. 571-661 ; and ' Description geologique 

 de la Montagne de Lure (Basses-Alpes),' 1888, Ann. des Sciences Geol. vol. xx. 

 pp. 110-169. 



3 E. Haug, ' Les Chaines subalpiues entre Gap et Digne ; Contribution a, 

 l'Histoire geologique des Alpes franchises,' Bull. Serv. Carte geol. France, 

 no. 21, vol. iii. (1891) pp. 169-191. 



4 Diener, ' Gebirgsbau der Westalpen,' pp. 190-218. 



