182 
POPULAR SCIENCE REVIEW. 
of which seems to he proved by the occurrence of masses of schist in the 
limestone. 
Ancient Eruptive Rocks of the Ruy-de-Dome. — M. A. Julien has communi- 
cated to the French Academy ( Comptes Rendus 28th March, 1881) some 
observations on the ancient eruptive rocks of the great plateau which bears 
the more modern volcanic formations of the Puy-de-Dome. His statement 
will probably be interesting to travellers in the Auvergne who pay atten- 
tion to geology. The rocks found are as follows : — Porphyroid granite, 
ordinary granite with grains of moderate size, leptynite (granulite of M. 
L6vy), pegmatite with tourmaline and garnets, amphibolic rocks, diorite, 
amphibolite, and amphibolic petrosilex. The porphyroid granite forms vast 
expansions, but all the other rocks are in the form of veins, which are very 
numerous and distinctly marked. The veins of leptynite and pegmatite have 
a general north and south direction, with slight deviations to the east and 
west. The veins of amphibolic rocks, on the contrary, generally run W.N.W. 
The order of appearance of these rocks was as follows: — First 
came outflows of porphyroid granite, which is the most ancient granite 
of the region ; then granite with modemte-sized grains in strong veins in the 
porphyroid granite ; then the veins of diorite. During the emission of the 
latter, amphibolic granites were injected between Aydat and Phialeix, and 
these again were traversed by veins of rose-coloured and green amphi- 
bolic petrosilex. Innumerable veins of leptynite afterwards appeared, and 
the pegmatites concluded the series of eruptive phenomena. The last two 
rocks are always quite distinct. 
The author states that all these relations are recognizable with the 
greatest clearness in many parts of this magnificent plateau; but he indicates 
certain points which he thinks of the most interest. 
1. At the Cotes de Ceyrat, along the road which ascends the flanks of 
the granite cliff to Berzet, the porphyroid granite contains enormous blocks 
of Cambrian schists. Very distinct veins of ordinary granite, some of them 
several metres thick, traverse the porphyroid granite. One of them in its 
course traverses one of the enclosed blocks. Veins of leptynite traverse both 
granites, and one of them also cuts through the same block of schist already 
traversed by the ordinary granite. 
2. In the quadrilateral included between Theddes, Chadrat, Saint-Genes, 
Champanelle, and Berzet, the porphyroid granite encloses hundreds of 
"Cambrian fragments, into which it is also injected in branching and anasto- 
mosing threads and veins penetrating the fissures of the blocks. The granite 
rmust therefore have been extremely fluid at the time of its production. 
'There is no trace of metamorphism ; innumerable N. and S. veins of leptynite 
and pegmatite traverse the whole system. 
3. Near Recolene, at 100 metres in front of the village, a magnificent 
wein of diorite enclosed in Cambrian quartzite, is distinctly cut through by a 
vein of leptynite 20 centimetres thick. 
4. Between Santeyras and Aydat, on the margin of the lake, there is on 
the road, 100 metres from Santeyras, a thick vein of diorite running N. 50° W. 
traversing the porphyroid granite and a large included mass of schist. 
This is in its turn cut by a vein of tourmaliniferous pegmatite 20 centi- 
metres in thickness. 
