Geological Age of the Carrara Marbles. 291 



% On Professor Bonney's first visit he did little more than examine 

 the quarried rocks and fragments, more or less water-worn, brought 

 down by the stream which debouches near the town of Carrara. On 

 his second visit he walked for some distance up the valley, collecting 

 specimens of the micaceous schists, often gneissic in aspect, which 

 were fairly common. All of these showed signs of crushing while in 

 a crystalline condition, and some a conspicuous cleavage-foliation. 

 He failed, however, to find any specimens of a marble with lines of 

 mica and chlorite (?) which he had seen built into the walls of the 

 Croce di Malta Hotel at Spezzia, or any marked signs of mechanical 

 disturbance in the pebbles of ordinary marble, most of which were 

 pure white, but some showed a lead-coloured clouding or streaking. 

 He then ascended to Miseglia, on the right bank of the valley, without 

 finding any good sections en route, owing to overgrowth, but ascer- 

 tained, especially in a quarry near this village, that an ordinary dark 

 limestone, with indications of mechanical disturbance (resembling 

 some near Spezzia and others of Jurassic age in the Oberland Alps), 

 which was associated with lighter-coloured varieties, occurred in close 

 proximity to normal Carrara marble. 



^f On this occasion he collected a few representative specimens of 

 the gneissose and schistose rocks, and one of the former had been 

 given to him, about 1885, by the late Professor Carvill Lewis. 1 

 This specimen, labelled by the donor " sericite- schist, Upper Triassic, 

 Carrara", has a gneissose aspect, and is obviously much crushed, the 

 curving cleavage surfaces glimmering as usual with a minute silvery 

 mica. 2 A transverse section exhibits zigzagging bands of two principal 

 constituents, the less abundant almost black, the other nearly white. 

 The latter, though sometimes rather like felspar, proves on examination 

 to be really quartz. The microscope shows that this mineral forms 

 rather polygonal grains, varying in size from about one-fiftieth of 

 an inch down to mere specks. The larger grains often occur in small 

 groups which are suggestive of broken-up veins. The quartz is 

 associated with an almost colourless mica. A few of the flakes are 

 about "01 in. long, having a faint brownish tinge, and giving bright 

 colours with crossing nicols, but the majority vary on either side of 

 •002 in. in length. These, I suspect, are produced by the shearing 

 of larger flakes. The dark mineral mentioned above often occurs in 

 more or less clustered granules, which so far as they have a definite 

 shape are slightly prismatic. They show a metallic lustre with 



1 I think he gave it to me shortly before my visit in the autumn of 1886, 

 remarking at the time : " Here is a gneiss of Triassic age from near Carrara." 

 My reply was to this effect : "If you had told me you got the specimen not far 

 from the St. Gotthard, on the northern side of the Val Bedretto, I should not 

 have been surprised. Was there in the field an actual sequence from it to 

 indubitable Triassic rock ? " "Not exactly," he a"nswered, "but they were 

 exposed on opposite sides of a valley." " Well, then," said I, "a fault may 

 have gone down that valley, so, though greatly obliged to you for the specimen, 

 I cannot admit that it has been proved to belong to the Triassic system." — 

 T. G. B. 



2 See Presidential Address to the Geological Society, Quart. Journ., vol. xlii, 

 Proc, p. 65, 1886. See also id., vol. xlvi, pp. 202-4, 1890, and other papers 

 of mine on Alpine schists. — T. G. B. 



