510 Prof. Bonney—Crystalline Schists of the Alpine Chain. 
remarkable ignorance on the part of certain foreign geologists.! 
Want of space prevents me from discussing in detail the petrological 
statements on pp. 158-62 of this volume, so that I must be content 
with saying that, when work in the field is checked by study with 
the microscope, the lessons of nature are clearer than those of the 
authorities followed by Dr. Preller. That the kinds of rocks 
mentioned by them occur in certain districts is no doubt true, though 
their nomenclature is sometimes confused ? and the suggested passages 
of one kind into another, where I have seen them, are due to the 
obliteration of their earlier history by intense crushing, or are 
consequences of thrust-faulting. For such a thing as the ascription 
of the cale-schists and crystalline limestones, with one group of the 
pietre verdi, to the Lias—Trias, and the mica-schists and minute 
gneisses, with another group of the same, to the Permo-Carboniferous 
(p. 807), no evidence is given; the matter at issue is quietly assumed. 
The general succession of the crystalline schists—micaceous, calcareous, 
and quartzose—and certain. gneisses I do not dispute, for I sketched 
it out thirty years ago,* and have upheld it ever since, though, as 
I hope, I have obtained a clearer knowledge of the pietre verdi group 
and of certain of the porphyritic gneisses, which are pressure-modified 
intrusive granites, later in date on the whole than the aforesaid 
rocks, but do not, so far as I have seen in the Western and Central 
Alps, cut Paleozoic or later sedimentary rocks. The above-named 
schists are fairly abundant on both sides of the Pennines, especially 
the northern, as in the mountain region around Saas, Zermatt, Arolla, 
and Zinal, also in the Lepontine, Rhetian, and Central Tyrol Alps; 
in fact, I have examined them in many places from the Viso to the 
Gross Glockner—quartz-schists, cale-schists, and mica-schists. These 
rocks form long continuous zones, in which ‘ green schists’ appear 
intermittently, and overlie a variety of coarser and stronger mica-schists 
and gneisses, below which are large masses of granitoid rocks, which, 
though apparently the older, are, in many cases at least, certainly the 
newer. But there is nothing to prove that the schists are of Trias— 
Lias age, only that here and there little strips, sometimes only a few 
yards in length and feet in breadth, are wedged in among the gneisses 
or crystalline schists. No one accustomed to the last-named group of 
rocks would have dreamt for a moment that the friable unaltered 
rauchwacké could possibly form part of one and the same series with 
1 Grou. MAG., 1901, p. 161. 
2 For instance, the schistes lwstrées have been for long a ‘‘ waiting-room ”’ 
where rocks in very different states of metamorphism are left till called for. 
* Q.J.G.S., 1886, Proc., p. 79. A generally similar succession of crystalline 
schists (originally sediments) occurs in the Highland zone between Dunkeld 
and Braemar, and hornblende schists (griiner schiefer of the coarser type) in 
the North-West Highlands. Id., pp. 91, 92. 
_ 4 Papers dealing with different points in the nature and succession of these 
rocks will be found in Min. Mag., 1887, pp. 1, 191; Gon. MaG., 1887, 
p. 573; 1889, p. 488; 1890, p. 533; 1893, p. 204; 1894, p. 114; 1896, 
p. 400; 1897, p. 110; Phil. Mag., 1892, p. 237; and Q.J.G.S., 1889, p. 67; 
1890, p. 187; 1893, pp. 89, 94, 104; 1894, pp. 279, 285; 1897, p. 16; 
1898, p. 357; 1903, p. 55; 1905, p. 690; 1908, p. 152. 
ce 
