Geological Age of the Carrara Marbles. 293 



sometimes include bands of mica from fully one-third of an inch in 

 thickness down to mere streaks. They also occur on the south side of 

 the Gorner Grat, near Pianura di Segno on the Lukmanier Road, to 

 the south of Spliigen village, and in the upper part of the Averser- 

 thal, associated with dark mica schists and calc-mica schists which 

 pass into white marbles. So far as I have seen, these quartz schists 

 generally occur low down in this group of the Upper Schists. 1 They 

 also have some resemblance to a quartz schist from a hill north of the 

 west end of Deny lea Lough, Connemara, 2 to one from Morone in the 

 Braemar district (though this rock shows less signs of crushing), and 

 still more to another one nearer that health resort. These quartz 

 schists present some resemblance to the highly crushed basal Cambrian 

 quartzite of Glendhu (Sutherland), in which, however, any argillaceous 

 constituent is less altered, and to crushed Torridonian near Kinlochewe 

 and Loch Clair, in which also mica is not so well developed, 

 fragmental felspar still remaining. 



^f A fourth specimen from the same valley is a schist with much 

 mica, slightly brown or greenish in tint, and quartz ; both small, the 

 latter slightly the more abundant, and the former showing sharp 

 waves or loops, with roughly parallel axes, as if a little more flexure 

 would have produced a strain-slip cleavage. Under a quarter-inch 

 objective, the quartzes are seen to be slightly elongated and the mica 

 almost colourless, but interspersed with it are rather numerous pale 

 umber-brown granules, slightly prismatic in form (? minute staurolites) 

 and a few which are opaque, probably an iron oxide. Three or four 

 prismatic grains, greenish-blue in colour and pleochroic, are probably 

 tourmaline. A fifth and smaller specimen so much resembles this one 

 that it has not been sliced. I have obtained rocks similar to these 

 from more than one part of the Alps where pressure has produced 

 conspicuous effects; occasionally from that 'waiting room' named 

 Casanna Schiefer, but more often from the Upper Schists. For 

 instance, they much resemble a specimen obtained between Mittersill 

 and Kitzbuhel on the southern side of the pass near the top. 



^f I have examined only a few slices of Carrara marble, because 

 I could not collect my specimens in situ. Those of the best marble 

 are granular in structure, consisting of crystalline calcite with 

 a variable amount of dolomite, showing some pressure twinning but 

 no signs of crushing; one of them containing two or three tiny 

 fairly idiomorphic quartz crystals. A specimen labelled " brecciated 

 marble, Seravassa" 3 is a crystalline dolomite. 4 It consists of pieces 

 or bands of coarser texture in a finer-grained matrix. The Carrara 

 marble is very similar to that from Pentelicus, 5 which, however, 



1 Quart. Journ. Geol. Soc, vol. xlv, p. 95, 1889. 



2 Perhaps also to the quartz-rock of the Twelve Pins, which I have not 

 actually visited. 



3 For which and other interesting specimens of marbles I have to thank 

 Mr. W. Brindley, of Westminster. 



4 In the Binn Valley crystalline dolomites are interbedded with dark mica 

 schists. 



5 This is asserted to be Cretaceous (Hatch and Eastall, ut supra, p. 250). 

 I have seen a little of this neighbourhood and am unable to accept the 

 identification. 



