NADLORE 
12! 
THURSDAY, DECEMBER 7, 1882 
RECENT RESEARCHES IN THE META- 
MORPHISM OF ROCKS 
N the heart of many mountain-ranges, and likewise 
spreading over wide hilly areas of the northern part 
of our hemisphere, lies the strikingly distinct series 
of rocks to which the name of The Crystalline Schists 
has been given. The passing traveller who knows nothing 
of geology cannot fail to be struck with their strange, 
crumpled and gnarled beds, through which streaks of 
white quartz wind and twist in a network of interlacing 
veins. Sheets of the naked rock often present a silvery 
sheen as sunlight falls across them, and this glistening 
aspect may be traced down in the minutest flakes of 
silvery mica that lie packed in parallel leaves throughout 
the mass. 
No group of rocks has given rise to more discussion 
than the Schists. An account of the oscillations of 
opinion regarding their origin would form a curious and 
interesting chapter in the history of geological speculation. 
They have been looked upon as parts of the aboriginal 
crust of the planet—traces of the first solid film that 
formed upon its fiery surface. By one school of writers 
they are believed to be original chemical precipitates 
from the waters of the primeval ocean. By another they 
are treated as masses of sedimentary or other material 
which have been crystallised and altered into their present 
condition by a process to which the name Metamorphism 
has been given. Between these two doctrines, with their 
various modifications, the pendulum of geological opinion 
has vibrated for somewhere about a century, and vibrates 
still. In England and America indeed, owing mainly to 
the commanding influence of Lyell, the metamorphic 
theery has so entirely prevailed that most English-speak- 
ing geologists have come to accept it as a demonstrated 
truth, and to look back upon the Wernerian doctrine of 
chemical precipitates as a singular and happily obsolete 
vagary of the geological imagination. They have written 
text-books in which that doctrine is not even so much as 
honoured with an allusion to its ever having existed, 
though here and there a solitary protest has now and then 
been raised among us in favour of the other view, like 
that uttered by De la Beche as far back as 1834, and 
those of Dr. Sterry Hunt in later years. In Germany, on 
the other hand, the old Wernerian dogma has always had 
its staunch adherents, but in gradually diminishing num- 
bers, the theory of the metamorphic origin of the crystal- 
line schists having been warmly espoused there also by 
an ever-increasing body of observers. 
For some years past what has been called the orthodox 
metamorphic doctrine has been called in question by 
various writers who have cast doubts on the observations 
which were believed to prove the fact that wide areas of 
rock, originally of fragmentary or detrital composition, 
had undergone a conversion into crystalline schists. The 
time-honoured doctrine of chemical precipitates, tricked 
out in the finery of modern chemical analysis, has been 
resusciiated and defended with the warmth of the most 
devoted partisanship. Within the present year, however, 
several memoirs have appeared which powerfully support 
VOL, XXVII.—No. 684 
the doctrine of metamorphism, and as effectively oppose 
the rival hypothesis. The aid of the microscope, as well 
as of chemical analysis, has been invoked : new facts and 
arguments have been adduced, and the nature of the 
changes involved in metamorphism have been more 
clearly made known. Whether or not there may be any 
crystalline schists in the earliest or Archzean rocks of the 
earth’s crust, which had their origin in the chemical 
precipitates of a primeval ocean, may remain a question 
for future discussion. But recent researches with all the 
manifold appliances of modern petrography demonstrate 
beyond the possibility of all further cavil, that ancient 
sedimentary strata have undergone such an alteration as 
to have assumed a more or less completely crystalline 
condition, that numerous silicates have been developed in 
them, often also with foliation, that these changes are 
seen round bosses of granite and other eruptive masses 
(contact metamorphism), but also far more strikingly 
over wide regions where eruptive rocks cannot have 
induced them (regional metamorphism), and that in the 
latter case the alteration is always connected with evi- 
dence of enormous mechanical pressure of the strata. To 
one or two of the more important recent papers, brief 
reference may here be made. 
The Silurian schists, with their fossils and remarkably 
compressed conglomerates in the Bergen district, have 
been made the subject of a remarkable memoir by Mr. 
Hans Reusch.! In this essay the author traces the 
passege from ordinary shales into fine phyllite-schists 
and mica-schists, in which crystalline aggregates of mica 
have been porphyritically developed. In some of the 
altered fossiliferous beds microscopic crystals of rutile 
and tourmaline have appeared. The fossiliferous lime- 
stones have been converted into marble, wherein, how- 
ever, the organic forms can still be detected. The fossils 
which occur in certain mica-schists, and have been speci- 
fically determined, leave no doubt that the whole series 
of rocks belongs to the lower part of the upper Silurian 
system. Yet they include intercalated bands of gneiss, 
hornblende-schist, talc-schist, and other foliated rocks. 
The author connects the crystalline condition of these 
masses with the effects of the enormous mechanical 
pressure which they have undergone, as shown, for 
example, by the extreme flattening of the pebbles in 
some of the associated conglomerates. 
The Silurian rocks of the Christiania district have 
long been famous for the illustrations they afford 
of the phenomena of contact-metamorphism. They 
have been subjected to a detailed investigation by 
Mr. W. C. Brégger, lately of the Geological Survey 
of Norway, and now Professor of Geology in the Uni- 
versity of Stockholm. He kas lately published what 
we hope is only an earnest of the valuable work we 
have yet to expect from him.* His monograph embraces 
the stratigraphy, paleontology, structure, eruptive rocks, 
and contact-metamorphism of the district. This last- 
named feature is more minutely traced out than has yet 
been attempted for that region, though only a beginning 
in the study has been made, Mr. Brégger deeming it 
* «Gilurfossiler og Pressede Konglomerater i Bergensskifrene.” (Chris- 
tiania: Universitets programm, 1882). This memoir was recently noticed in 
these columns (NATURE, vol. xxvi. p. 567). 
2 «Die Silurischen Etagen 2 and 3 im Kristianiagebiet und auf Eker.’ 
(Christiania: Universitétsprogramm, 1882). 
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