Parr VIII §2.] LOCAL METAMORPHISM. 579 
limestones have their carbon dioxide replaced by silica in a broad zone 
of lime-silicate along the contact.’ 
In the Christiania district of southern Norway instructive illustrations 
of the metamorphism of sedimentary rocks round eruptive granite have 
long been known. Kjerulf has shown that each lithological zone of the 
Silurian formations as it approaches the granite of that district assumes 
its own distinctive kind of metamorphism. The limestones become 
marble, with crystals of tremolite and idocrase. The calcareous and 
marly shales are changed into hard, almost jaspery, shales or slates; 
the cement-stone nodules in the shales appear as masses of garnet; the 
sandy strata become hard siliceous schists (Halleflinta, jasper, hornstone) 
or quartzite; the non-calcareous black clay-slates are converted into 
chiastolite-schists, or graphitic schists, but often show to the eye only 
trifling alteration. Other shaly beds have assumed a fine glimmering 
appearance ; and in the calcareous sandstone, biotite has been developed. 
In spite of the metamorphism, however, neither fossils nor stratification 
have been quite obliterated from the altered rocks. From all the strati- 
graphical zones fossils have been found in the altered belt, so that the 
true position of the metamorphosed rocks admits of no doubt.? 
Round the granite bosses of Devon and Cornwall, Devonian and 
Lower Carboniferous strata have undergone similar metamorphism.? 
In the lake district of the north of England excellent examples of the 
phenomena of contact may be observed round the granite of Skiddaw. 
The alteration here extends for a distance of two or three miles, from 
the central mass of granite. The slate where unaltered is a bluish-grey 
cleaved rock, weathering into small flakes and pencil-like fragments. 
Traced towards the granite, it first shows faint spots, which increase in 
number and size until they assume the form of chiastolite crystals, with 
which the slate is now abundantly crowded. The zone of this andalusite- 
schist seldom exceeds a quarter of a mile in breadth. Still closer to the 
granite a second stage of metamorphism is marked by the development 
of a general schistose character, the rock becoming more massive and 
less cleaved, the cleavage planes being replaced by an incipient foliation 
due to the development of abundant dark little rectangular or oblong 
spots, probably imperfectly crystallized chiastolite, this mineral, as well 
as andalusite, occurring also in large crystals, together with minute 
flakes of mica (spotted schist, knotenschiefer). A third and final stage 
is reached when, by the increase of the mica and quartz-grains, the rock 
passes into mica-schist—a light or bluish-grey rock, with wonderfully 
contorted foliation, which is developed close to the granite, there being 
always a sharp line of demarcation between the mica-schist and the 
granite,* 
Farther north in the south-western counties of Scotland several large 
masses of fine-grained granite rise through the Lower Silurian grey- 
wacke and shale, which, around the granite for a variable distance of a 
few hundred yards to nearly two miles, have undergone great alteration. 
1 Zincken, Karsten und v. Dechen. Archiv. v. p. 345; xix. p. 583. Fuchs, N. Jahrb. 
1862, pp. 769, 929. K. A. Lossen, Z. Deutsch. Geol. Ges. xxi. p. 291; xxiv. p. 701. 
Kayser, Op. cit. xxii. p. 103. The memoirs of Lossen form some of the most important 
contributions to our knowledge of the phenomena of metamorphism. 
* Kjerulf, “ Geologie Norwegens,” 1880, p. 75. . 
3 De la Beche, ‘ Geology of Devon and Cornwall,’ Geol: Surv. Mem. i. 1839. 
4 J.C. Ward, Q. Journ. Geol: Soc. xxxii; (1876), p. 1; 2 P 
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