Dr. Du Riche Preller—Crystalline Rocks, N. Prémont. 318 
Chatillon and Verrés in the Dora Baltea Valley and thence up the 
Tournanche and Brusson Valleys, whence it skirts the base of 
Matterhorn and Monte Rosa. 
4, Mont Mary.—On the left of the Dora Baltea north of Aosta, 
and exactly opposite Monte Emilius, rises the Mont Mary (2,875 m.) 
group, which is the counterpart of the former and exhibits a similar 
reversed sequence. ‘he calc-schist appears here at the base, and is 
overlain by Permian schist, upon which rests the cupola of garneti- 
ferous mica-schist. The group, which includes Gran Becca 
(2,967 m.) and Gran Col (2,864 m.), lies in the zone of the same 
fracture fault and presents the same phenomenon of an inverted fold 
as Monte Emilius on the opposite side of the valley. From the 
Mont Mary group the mica-schist formation extends up Val Pellina 
and across the crest of the Pennine Alps to Dent Blanche (4,364 m.), 
north-west of Matterhorn.! 
The great intrinsic geological interest of the crystalline rock-areas 
of the Aosta valleys described in the foregoing has in recent years 
been enhanced by Lugeon and Argand having included them in their 
grand series of overthrust sheets in that and other parts south of the 
crest of the Alps.? According to their theory, worked out from 
ingenious geometrical designs, the Gran Paradiso, Grivola, Grand 
Nomenon, Emilius, Rafré, and Mary groups are not ‘‘ rooted” or 
‘‘autochthonous’’ massifs, but cover-sheets (nappes de recouvrement) 
pushed over from different directions and more or less considerable 
distances. Investigations instituted by the Italian Geological Survey 
in 1905,5 and notably by Novarese in 1909,* have, however, 
conclusively shown that the cupolas of those groups differ strati- 
graphically and lithologically from the ‘‘ root”? areas whence they 
are supposed to have been derived, and that, with the exception of 
the small, isolated massif of Monte Pilonet (2,697 m.) between the 
Tournanche and Brusson Valleys on the left of the Dora Baltea, 
‘where the gneiss cupola completely covers the cale-schist, there is no 
evidence at all of extensive overthrusts in that part of the Alps. 
1 VY. Novarese, ‘‘ Gneiss Monte Emilius e M. Mary’’: Boll. Soc. geol. ital., 
1912, p. 31. Novarese describes an interesting section of granite, mica-schist, 
and diorite i in a railway cutting ne wmeea Aosta and Quart, on the left of Dora, 
below M. Mary. 
2M. Lugeon & E. Argand, ‘‘ Grandes Nappes de Recouvrement de la 
zone du Piémont. Homologies ditto’’ : Comptes rendus Acad. Sciences, Paris, 
Mai 15 et 29, 1905. 
3 “*Relazione’’: Boll. R. Com. geol., 1906, p. 27. 
4 V. Novarese, ‘‘ Profilo Grivola’’: Boll. R. Com. geol., 1909, p. 497 et seq. 
A. Stella, op. cit., 1912, p. xlvi. ‘‘ Problema geo-tettonico Ossolae Sempione”’ : 
Boll. R. Com. geol., 1905, p. 5 et seq. S. Franchi, “‘ Tettonica della Zona 
del Piemonte ’’: ibid., 1906, p..123 et seq. 
(To be concluded in our next Number.) 
