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XXVI. On the Equivalents of the Cambrian and Silurian 

 Systems i7i Belgium ,- embodied in a *' Report on the Progress 

 of the Geological Map of Belgiiwif during the year 1838." 

 By A. H. DuMONT, Member of the Royal Academy of 

 Sciences of Bjyissels.* 



THE ancient tracts of Belgium are beyond contradiction the 

 most important, whether viewed in a scientific light, that 

 is to say, as regards the divisions which mineralogy and pa- 

 laeontology enable us to establish, or commercially, on account 

 of the riches in combustibles and metalliferous ores which 

 they contain. 



From these considerations the Academy will doubtless 

 find that it was desirable not only to make known the dif- 

 ferent modifications which these tracts present, but also their 

 relations to the other analogous districts in neighbouring 

 countries. 



In 1837 and 1838, I called the attention of the Academy 

 to the agreement which exists between the formations of 

 the Eifel and the two lower systems of the anthraxiferous 

 districts of Belgium. 



This year I have endeavoured to make the same compari- 

 sons between our systems and those which Mr. Murchison 

 has recently established in Great Britain. 



For this purpose, 1 undertook, along with our learned col- 

 league M. d'Omalius d'Halloy, and M. de Verneuil, a distin- 

 guished palaeontologist, a special journey into Wales, and I 

 think that I have succeeded in establishing a complete paral- 

 lelism between the English formations and our own. 



The west of Great Britain completely reminds us of the 

 south-east of Belgium. We find there the cultivated hills of 

 Condros, and the barren plains of the Ardennes, which agree 

 in the composition of their rocks with the divisions established 

 by Messrs. Murchison and Sedgwick, under the name of the 

 Silurian and Cambrian systems, corresponding exactly to those 

 which M. d'Omalius designated, in 1808, by the names of 

 slaty and anthraxiferous [ardoisicr ct anthrax if ere). 



If we survey the Cambrian district, it is easy to recognise 

 two systems there, distinct, as much by their I'elative position 

 as by their mineralogical composition. The first which I 

 observed amongst others in the neighbourhood of Dinas 

 Mowddwy, forms the central mass of Wales, and presents a 

 number of rocks which may be considered as true slate, and 

 which in a great many places are worked. This mass an- 



* From the Bulletins deP Academic Royale des Sciences, Sfc. de Bnixelles. 

 Vol. V. p. 634. 



