122 
NATURE 
| Dec. 7, 1882 
better to publish his first results now than to wait for 
leisure to extend and complete them. He points out, as 
had already been done by Kjerulf and others, that while 
there isa general alteration as the rocks approach the 
eruptive masses of granite and syenite, the special type 
of alteration depends in each case upon the original 
capacity of the rock for metamorphism. He has traced 
the Silurian zones from their ordinary unaltered condition 
until they assume their most metamorphosed character 
against the granite, and he compares the chemical com- 
position and microscopic structure of the unaltered and 
altered strata. He points out that certain bands of rock 
appear to be endowed with a remarkable capacity for 
withstanding the effects of metamorphism. 
Dictyograptus-shales may be observed close to the granite 
and in the midst of the most intensely-metamorphosed 
beds, yet comparatively little changed. They become 
paler in colour and perhaps somewhat harder and more 
compact, but their graptolites are as well preserved, down 
even to the minutest details, as they are at a distance from 
the contact-zone. The dark alum-shales are converted 
into hard compact bluish “ Knotenschiefer’’ and chias- 
tolite-slates, still retaining their fossils. The chiastolite 
crystals may even be seen traversing the graptolite-stems, 
which are otherwise as well preserved in these as in the 
ordinary unaltered shales. The remarkable development 
of silicates in the Christiania limestones, where these 
rocks have been converted into marble near the granite, 
has long been a classical instance of contact-meta- 
morphism. Mr. Brogger gives some interesting observa- 
tions of his own among these rocks. He notes the 
occurrence of recognisable fossils even in those parts of 
the marble where the silicates have been abundantly de- 
veloped, and he points to the suggestive fact that where 
a fourth or fifth part of the marble is made up of red 
garnet, the latter mineral, in well crystallised rhombic 
dodecahedra, may be found inclosing the valve of an 
Orthis calligramma. 
The alternation of comparatively little-changed grapto- 
lite shales with fine crystalline schists and forms of horn- 
fels, which Prof. Brégger reports from so many localities, 
is a fact of great significance in relation to the problem 
of the origin of the crystalline schists. That the crystal- 
line character has been superinduced upon what were 
once ordinary marine mechanical sediments admits now 
of no doubt. The extent of the change appears on the 
whole to depend on the one hand upon the liability of 
the rock to metamorphism, and on the other upon relative 
proximity to the eruptive rock. The preservation of 
organic remains in the altered bands is exceptional, and 
depends, according to our author, Ist, upon the greater 
permanence of the substance of the organisms, the chitin 
of the graptolites, for example, being apparently undis- 
tingu shable in the altered beds from the same substance 
in the ordinary shales ; 2nd, upon the replacement of the 
hard parts of the organisms by mineral matter, either 
before or during the process of metamorphism ; and 3rd, 
upon the filling up of the original cavities of the fossils 
by some mineral, as graptolites by pyrites, and the interior 
of brachiopods by wollastonite, or upon the inclosing of 
the organisms in a crystalline matrix as in the case of the 
impressions of shells in garnet, just referred to. But, asa 
rule, fossils disappear even from the most richly fossiliferous 
Thus the | 
bands as these are traced across the altered zone. Mr. 
Brogger modestly regards his observations as still too 
limited to warrant him in theorising on the phenomena of 
contact metamorphism. But the admirable methods he 
has followed, connecting in one broad microscopical and 
chemical research both the altered and unaltered con- 
dition of the same rock, mark a new starting-point for 
the further study of that "great geological problem— 
metamorphism. 
There is one further incidental but pregnant statement 
in this Memoir to which reference must here be made. 
So far back as the years 1875 and 1877 Prof. Broégger, in 
the course of his field-work in the Geological Survey of 
Norway, established the existence of graptolite-bearing 
beds among the crystalline schists of the Hardanger 
region. He now publishes some details of the section 
there visible, from which we learn that the graptolite band 
(Dictyograptus-schiefer) occurs among some Dlack little 
altered alum-slates lying at the very base of the enormous 
series of crystalline schists forming the Norwegian high- 
lands! The alum slates pass under some bluish quartzose 
sandstone, overlaid by a white impure marble (possibly 
the Orthoceratite limestone), which in turn is covered by 
greenish micaceous clay-slates (phyllites). Above these 
basement strata come more and more crystalline schists, 
comprising diorite-schists, hormblende-schists, garneti- 
ferous mica-schists, foliated rocks of many varieties, and 
true gneisses—the two last mentioned rocks sometimes 
several thousand feet thick. We learn further that in 
1877 the same observer, in harmony with Naumann’s 
observations, established the fact that the enormous 
series of crystalline schists of the Norwegian mountains 
is younger than the second stage of the Silurian (or Cam- 
brian) rocks of the Christiania district. He refers to his 
friend Mr. Reusch’s discovery of Upper Silurian fossils 
from the crystalline schists of Bergen, asa confirmation of 
his former supposition that the whole of the vast succession 
of crystalline schists in the Norwegian mountains is a 
metamorphic series. 
When we remember that on the- opposite side of the 
peninsula similar primordial fossiliferous strata emerge 
from underneath the vast overlying schists and crystalline 
rocks of the Swedish uplands,* it is evident that an 
enormous area of regional metamorphism extends across 
Scandinavia. The close parallel between the structure of 
this region and that of the Scottish Highlands is one of 
the most striking facts in the geology of North-Western 
Europe. In both areas recognisable Silurian fossils occur 
at the very base of the vast metamorphic series, and the 
rocks become progressively more and more crystalline as 
they are traced from bottom to top. 
A third remarkable paper by Pére Renard, of the Royal 
Museum, Brussels, must be cordially welcomed as one of 
the most important contributions of modern petrography 
to the study of metamorphism.’ It deals with a portion 
of the singular belt of crystalline schists which runs 
through the French and Belgian Ardennes. Dumont as, 
far back as the year 1848, published an account of these 
rocks, the significance of which that accurate observer 
fully perceived. He showed that they occur in his 
I x See A. E. Térnebohm, Bihang till Svensk. Akad. Handl., 1873. 
“Les Roches Grenatiféres et Amphiboliques de la region de Bastogne,’ 
par A. Renard, Budletin du Musée Royald' Histoire Naturel de Belgique, 
tome i. 1882. 
