﻿RevieiDs — Poussin Sf Renard — Belgium 8f the Ardennes. 175 



are by one of the founders of the new science — H. Clifton Sorby, 

 r.E.S. Only the other day a Greological Survey Memoir 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 same 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. Eose, 

 Tschermak, Zirkel, Kenngott, Vogelsang, Mohl, Borioky, 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. In France the impulse has been felt, although 

 not so strongly, and is rapidly spreading 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 untouched. 

 Andre Dumont had long ago described the physical relations of the 

 so-called " Plutonic " rocks of the Ardennes and the Ehine, and 

 d'Omalius d'Halloy has left valuable notes on some of them. Quite 

 recently also Prof. Malaise published a paper " On some of the 

 Porphyritic Eocks of Belgium," which cleared up many errors, and 

 brought to light a number of new facts ;^ but, armed with the micro- 

 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 French 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 sedimentary 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, Eebecq-Eognon, Pitet, 

 and Steenkuyp, 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 BuUetins Acad, royale de Belgique, 2^^e ser. t. sxxviii. 



