408 Dr. Du Riche Preller—Contact-Zone of 
1912.! Discarding Rovereto’s local and partial ovérthrust as too 
timid, incomplete, and wanting in precision, they argue with 
characteristic entrain and incisive style and treatment in favour of 
a comprehensive overthrust of exotic, long distance origin, and from 
that point of view the subject is worked out so thoroughly that it 
will be interesting to outline its salient points. © 
(1) The extensive examination of the area by the authors leads 
them to extol the Savona crystalline massif as an ideal ‘ cover-sheet’ 
region, which, in point of transport and overthrust phenomena, they 
consider the most typical, unique, and classic of its kind in Europe. 
All along the roads, in the ravines, and on the heights they find in the 
abundant examples of intense crushing, lamination, brecciation, and 
friability of the crystalline masses conclusive evidence that these 
masses were, by subterraneous transport from an exotic source, 
wedged between the two sedimentary—the Permo-Carboniferous and 
the Triassic—formations of the Savona Hills, and thus became the 
dividing and contact-zone between the Alps and the Apennines. 
(2) While wholly adopting Rovereto’s view of the Savona and 
Santuario Permo-Carboniferous ‘window’, the authors dissent from 
his lithological distribution of the crystalline rocks, and regard the 
massif as in the main composed of granitic and only to a very minor 
extent of gneissic and amphibolic rocks, the proportion of the three 
being, according to their estimate, respectively 2, 4, and %.?_ In this 
estimate they also include a good deal of Permian schist which they 
regard as altered granitic rock. Of the enormously predominant 
granitic masses, as also of the gneisses and amphibolic rocks, only a 
small part is intact and unaltered ; the great bulk is altered, 
structurally and mineralogically, to. mylonites, viz. bruised, crushed, 
laminated, mashed, and brecciated by friction of transport and by 
dynamic pressure. 
(3) The granite when fresh contains 68 per cent of silica and in 
chemical composition comes near to that of Mont Blanc, but nearer 
to that of Elba, where Termier already previously claimed extensive 
granite areas as mylonites,® which he correlates with and quotes in 
support of the phenomena in the Savona region. Of the mylonitic 
granite the authors enumerate seven varieties or stages between 
fresh unaltered granite and the most advanced mylonitic rock as the 
other extreme. The first four stages comprise the fissured and 
brecciform, the partially crushed and laminated, the intensely 
laminated, and the incompletely crushed but not laminated rocks, 
1 P. Termier & I. Boussac, ‘‘Le Massif Crystallin Ligure’’: Bull. Soe. 
géol. France, 1912, p. 272 et seq., with map and 2 sections, preceded by two ~ 
preliminary notes of 1911. 
2 Rovereto’s distribution of granite, gneiss, and amphibolites may be 
estimated from his map as 3%, 7%, and jy respectively, his granite area being 
less than half that of Termier & Boussac. 
3 P. Termier, ‘‘ Tectonique de l’Ile d’Elbe’’: Bull. Soc. géol. France, 1910, 
p- 314 et seq. The conclusions of this memoir were contested by B. Lotti, 
‘‘ Tipotesi del Termier sulla tettonica Isola d’Elba,’’ Boll. R. Com. geol., 
1910, p. 284 et seq. ; and by V. Novarese, ‘‘ I] presunto piano mylonitico del- 
V’Isola d’Elba,’’ ibid., 1910, p. 292 et seq. 
