Rerieics — Pomsin 4 * Renard — Belgium fy the Ardennes. 175 
are bv one of the founders of the new Science — H. Clifton Sorby, 
F.R.S. Only the other day a Geological Survey Memeir was issued, 
a chief feature of which is the delineation of the microscopic 
structure of some of the rocks of the Lake District, leading to 
important conclusions. In this case the field geologist and the 
microscopist were one and the sarne person, but this is the ex- 
ception. It is in Germany that this line of inquiry has attracted 
the greatest attention. There the influence of such men as G. Rose, 
Tschermak, Zirkel, Kenngott, Vogelsang, Möhl, Boricky, von Lasaulx, 
and a host of others has been such that not only have manuals 
of micro-petrography been published and sold, but that special 
Chairs for the teaching of the subject have been established in most 
of the Universities. ln France the impulse has been feit, although 
not so strongly, and is rapidly spreadiug under the influence of 
Delesse, Des Cloizeaux, and Michel-Levy. Now we have to record 
a brilliant beginning on the part of Belgium in the handsome memoir 
the title of which heads this notice. 
The authors, both Professors, one at the Catholic University of 
Louvain, and the other in the Jesuits’ College in the same town, 
thoroughly deserve the gold medal with which their work has been 
rewarded by the Academy of Belgium, and the extremely beautiful 
coloured plates with which it has been liberally furnished by that 
body. 
The subject worked out by them was not absolutely untouclied. 
Andre Dumont liad long ago described the physical relations of the 
so-called “Plutonic” rocks of the Ardennes and the Rhine, and 
d’Omalius d’Halloy has left valuable notes on some 6f them. Quite 
recently also Prof. Malaise published a paper “ On some of the 
Porphyritic Rocks of Belgium,” which cleared up many errors, and 
brought to light a number of new facts ; 1 but, armed with the rnicro- 
scope and their German method, the Louvain Professors have by their 
prize-memoir marked an era in the progress of Belgian geology. 
We say geology advisedly, for although their procedure is litho- 
logical and mineralogical, yet their most interesting results are 
strictly geological. Thus they show that. the amphibolitic and 
porphyroidal rocks of Frencli Ardenne are regularly interbedded 
with the Cambrian slates and quartzites amongst which they lie, and 
that they are not intrusive, as they were long considered to be, but 
are of truly sedhnentary origin. They hazard the opinion that the 
crystallization of these rocks took place at the bottom of the sea, 
very soon after their deposition, and when the materials were still 
in a plastic state. In the same manner, the schistoid eurite of 
Enghiem, the quartzose eurite of Nivelles with ripple-marks. the 
porphyroidal rocks of Monstreux, Fauquez, Rebecq-Rognon, Pitet, 
and Steenkuvp, all of which were looked upon as igneous, are proved 
to be derivative deposits. The Lower Silurian arkoses of Brabant 
are shown to be, not strongly metamorphic, but formed of trans- 
ported crystallized materials only. The so-called “ Hypersthenite ” 
1 See Bulletins Acad. royale de Belgique, 2< ;,me ser. t. xxsviii. 
