214 NATURE 
7 
Sitzungsberichte der Naturwissenschafilichen Gesellschaft Isis, 
Dresden, 1884.—Osteology of Rana temporaria, L., and Rana 
esculenta, L., by H. Reibisch.—Note on Yestadinaria elephant- 
pes, Lindl., and Welwitschia mirabilis, Hook, by Prof. O. 
Drude.—Biographical notices of the late Dr. H. R. Goppert of 
Breslau, of F. von Hochstetter of Vienna, and of Dr. W. 
Gonnermann of Coburg, by Dr. Geinitz.—Mineralogical and 
geological results of a journey to Italy in the year 1884, by A. 
Purgold.—On a prehistoric necropolis at Trog, near Rosegg, 
Carinthia, by W. Osborne.-—On some metal objects recently 
discovered at Jessen, near Lommatsch, by Dr. Caro.—On the 
increase of accidents from lightning in the Kingdom of Saxony, by 
Johannes Freyberg.—Remarks on some urns and other archzo- 
logical remains lately discovered at Uebigau, near Dresden, by 
Dr. J. von Deichmiiller.—Memoirs on the phanerogamous flora 
of the Voigtland district, Saxony, by A. Artzt.—On the granites, 
gneiss, crystallised limestones, schists, and other primitive 
rocks occurring in the districts north of the Zittau and Jeschken 
ranges, by Emil Danzig. 4 
——_—__.__-__.__ —_-@ —— ees 
Rendiconti del Reale [stitute Lombardo, May 7.—Results so 
far obtained from the study of the chief ichthiofauna of the 
Cretaceous period, by Prof. F. Bassani. This elaborate mono- 
graph concludes with a comparative table of the fossil fishes of 
Pietrarvia, Voirons, Comen, Lesina, Crespano, Monte S. 
Agata, Grodischtz, Tolfa, and Hakel.—A contribution to the 
study of etherification by double decomposition : formation of 
the nitrous ether of allylic alcohol, by Prof. Giacomo Bertoni. 
—Further remarks on the functions which satisfy the differential 
equation A’ = 0, by Prof. Giulio Ascoli.mRemarks on the 
modifications introduced by the present Minister, Pessina, into 
the Penal Code proposed by Savyelli, by E. A. Buccellati. 
SOCIETIES AND ACADEMIES 
LONDGN 
Royal Society, June 18.—‘‘ Regional Metamorphism,” by 
Joseph Prestwich, M.A., F.R.S., Professor of Geology in the 
University of Oxford. 
Metamorphic rocks have been divided into two classes—(r) 
Those in which the change has been caused by contact with 
heated eruptive rocks ; (2) Those extending over wider areas, in 
which the rocks are in no apparent relation to eruptive or 
igneous rocks. The first has been termed Contact Metamiorphism, 
and the second Wormad or Regional Metamorphism, the latter two 
terms having been used to express the same phenomena and 
treated as synonymous, 
The author, however, for reasons to be assigned, pro- 
poses, while retaining the use of both the latter terms, to 
apply them differently. Normal metamorphism he would con- 
fine, as hitherto, to the changes caused by the heat due to 
depth, on the supposition of the existence of a heated central 
nucleus of the earth, while he would use the term 7egzonal meta- 
morphism to denote changes effected by tlie agency of the 
physical causes to which Mr. Mallet referred the fusion of the 
volcanic rocks, namely, the heat produced locally within the crust 
of the earth by transformation into heat of the mechanical work of 
compression, or of crushing of portions of that crust. 
The primary object of Mr. Mallet’s experiments was to 
ascertain the force required to crush portions of various rocks of 
viven size, and to determine the quantity of heat evolved by the 
process. For this purpose the work done was measured by the 
uumber of cubic feet of water at 32° F. that could be converted 
nto steam of one atmosphere (or at 212° F.) by the estimated 
heat evolved by the crushing of 1 cubic foot of each class of rock. 
With all the harder rocks the heat produced in the metal sur- 
roundings by the complete crushing was easily perceptible by 
the hand, and was so great with some of the granites and 
porphyries as to necessitate a delay for the apparatus to cool. 
30th Mr. Mallet and Prof. Rankine were of opinion that in the 
crushing of a rigid material such as rock almost the entire me- 
chanical work (with the exception of a small residue of external 
work) reappears as heat. It was further shown that, even in 
the most rigid bodies, crushing begins by compression and 
yielding, and that at this stage heat begins to be evolved. 
Consequently the work thus developed being transformed into 
heat, that heat will be greatest along those lines or planes at 
places where the movement and pressure, together constituting 
the work, is greatest ; whence Mallet concluded that along or 
about such axial lines of concentrated compressive and crushing 
work the temperature may locally rise to a red heat, or even to 
that of fusing the rocky materials crushed and of the pressing- 
together-walls themselver adjacent to them. This was in his 
opinion the real nature and origin of the volcanic heat as now 
produced on the globe. 
Although the hypothesis fails for various reasons in its appli- 
cation to vulcanicity, especially for the reason that the great 
lines of disturbances and compression of the Alps, Pyrenees, 
and other mountain chains are free from either active or extinet 
volcanoes, there is, nevertheless, reason to believe that this 
source of heat may have been adequate to produce great mole- 
cular changes in the rocks along the lines of disturbance and 
upheaval, though the extreme results obtained by entire crushing 
by mallet would rarely or ever occur in nature. It is, however, 
precisely along such lines that not only are older rocks meta- 
morphosed, but rocks of Cretaceous and Tertiary age—which 
usually have not been affected by normal metamorphism— 
coming, in these mountain-chains, under the influence of the 
disturbing forces, have undergone a change analogous to that 
produced by normal metamorphism. 
Objections have been raised to the explanation offered in some 
cases of alteration of sedimentary strata in mountain-chains by 
ordinary normal metamorphism, on the grounds that unaltered 
strata alternate with altered strata. Sometimes this may be 
explained by inyersion of the strata, or, where that is not the 
case, it may be due to the circumstance that differences 
of mineral composition, or in the proportion of the water of im- 
bibition, have caused the metamorphism to affect different beds 
in different degrees. On the theory of regional metamorphism, 
in the sense the author would use it, another explanation sug- 
gests itself by the way in which differences in the resistance of 
the rocks develop different quantities of heat. Mr. Mallet has 
shown by experiments on the compressibility of rocks at Holy- 
head that, although certain slate-rocks were compressed by pre- 
cisely the same force before their elastic limits were passed, yet, 
owing to differences in their compressibility, the heat developed 
in the rocks when released would render the quartz-rock nearly 
three times as hot as the slate-rock. In this manner, therefore, 
it seems possible to account for a special and restricted meta- 
morphism of the strata in mountain-chains, and for its frequently 
localised occurrence. 
The remarkable changes which take place in the condition 
of the coal of Pennsylvania, as it ranges into the Appalachian 
Mountains, may also be owing more probably to 7zgiona/ than 
to normal metamorphism. This mountain-range consists of a 
series of great parallel folds increasing in acuteness as the central 
axis is approached. Eruptive rocks are absent, but, neverthe- 
less, the strata as they approach the central chain become more 
crystalline, and the coal, which at a distance is ordinary bitu- 
minous coal, passes into anthracite and even graphite. The 
late Prof. H. D. Rogers divided this great coal-field into four 
basins. The coal in the less-disturbed district near the Ohio 
River, where the flexures are extremely gentle and wid2 apart, 
contains from 40 to 50 per cent. of volatile matter; in the wide 
basin further east it decreases to 30 or 35 per cent.; in the 
basins of the Alleghany range, in which, although there are no 
important dislocations or great flexures, there are some extensive 
and symmetrical anticlinal axes of the flatter form, the propor- 
tion of the volatile matter in the coal varies from 16 to 22 per 
cent. ; while in the most easterly chain of basins which are 
associated with the boldest flexures and greatest dislocations, 
with close plications and inversions of strata, the quantity of 
volatile matter in the coal is reduced to 6 to 14 per cent. 
A somewhat analogous instance is presented by the Carboni- 
ferous series of Belgium. The excessive squeezing, faulting, 
and inversion which the Coal-measures have undergone on the 
flanks of the axis of the Ardennes, is there accompanied by an 
alteration of the highly bituminous coals into dry coals and into 
anthracite; while the Carboniferous and Devonian limestones 
amidst the sharply convoluted and folded strata of the Ardennes 
are there, as they are also on the line of the same disturbance in 
the Boulonnais, transformed very generally into crystalline 
marbles. The few exposures of eruptive rocks are all on a 
small scale, and affect the adjacent rocks only by contact meta- 
morphism. It is probable that the anthracite of South Wales is 
the result of similar egional metamorphism. 
In the case of contact metamorphism the changes were pro- 
duced by great heat, for the eruptive rocks must have had a 
temperature of 3000° to 4000" F. or more ; while in the case of 
normal metamorphism it is evident that the changes produced 
[Fuly 2, 1885 
