430 Reviews — Dr. Mourlon — Geology of Belgium. 



down to a great extent an the same lines as Dewalque's Prodrome, 

 which is another way of saying that it is admirabl}'^ planned. 



The first volume is stratigraphical, and consists of clear and 

 well-proportioned descriptions of all the rocks of the country, in 

 ascending order. In most cases the views of other authors are very 

 fairl}' stated and discussed, whether they be or not those held by 

 Dr. Mourlon himself, and justice is done to even the very latest 

 discoveries. We shall endeavour to point out the chief subjects 

 referred to which are the outcome of work published since 1868, and 

 which, therefore, may be looked upon as the justification of the 

 book. 



In the first place we find the important researches of Messrs. 

 Eenard and de la Vallee Poussin on the micro-petrography of the 

 Ardennes igneous and metamorphic rocks duly recorded and 

 illustrated by two capital tinted plates of microscopic sections, some 

 of which are given here for the first time. The divisions of the 

 Cambrian {^Salmian, Revinian, and Devillian) are next considered, and 

 the modern views of Dewalque, Gosselet, and Malaise compared with 

 those of Duraont — nor is the correlation of these rocks with the 

 Tremadoc Slates, Lingula Flags, Llanberis Slates, and Harlech Grits 

 of Wales determined by the first-named writer overlooked. Among 

 the Silurian rocks new matter of importance is included which is 

 principally due to M. Gosselet and to the author himself. It is, 

 however, in the account of the Devonian deposits that the value of 

 the work done by both these geologists becomes most apparent, 

 indeed the former may be said to have thoroughly mastered the 

 many difficulties which beset the study of the Lower and Middle 

 divisions [Gedinnian, Coblentzian, Ahrian, Eifelian), whilst the upper- 

 most Devonian (the Psammites de Condroz), which many in Britain 

 would prefer to regard as Lowest Carboniferous, has been equally 

 completely dealt with by M. Mourlon. 



On reaching the Carboniferous Rocks proper, justice is done to the 

 recent investigations of Hull and Hai'dman, and Eenard as to the 

 origin of the chert so common in the Limestone Series, and to those 

 of Dupont as to the division of that series, as developed in Belgium, 

 into six members, each clearly defined paleeontologically and, it 

 would seem, also stratigraphically. Some of these members of the 

 series appear to be often wanting, and it must be confessed that to 

 any one accustomed to the Lower Carboniferous rocks of Britain, M. 

 Dupont's maps of the Dinant district, in which these beds are shown 

 as in a very network of faults, none of which is marked as doubtful, 

 are apt to look as if they had been drawn up on somewhat too 

 theoretical grounds. We cannot help thinking that Prof, de 

 Koninck's old division into three may still be the more useful. 

 The Coal-measures, considering their commercial importance, and 

 the great interest attaching to the peculiarities of their lie in 

 Belgium, are somewhat cursorily dismissed. Nevertheless their 

 chief features are described, the flora discussed with reference to 

 the work of Coemans and Crepin, and the faults, natural pits, etc., 

 with reference to that of Cornet and Briart, and others. 



