148 M. Dumont on the Equivalenis of the Cambrian 



Wenlock limestone is found to occupy but a very small space, 

 to narrow progressively towards the south-west, so as to be re- 

 duced near Ludlow, to a breadth of six miles, and further 

 on to lose itself in the schist. 



But if the calcareous rocks are much more developed in 

 Belgium than in Great Britain, the schistose and psammitic 

 rocks are on the other hand much more prevalent in the 

 latter country. 



I have yet to speak of a very considerable deposit, which 

 prevails principally in the counties of Hereford and Brecon, 

 and to which the name of old red sandstone has been given. It 

 is doubtfid v/hether this formation has a representative in Bel- 

 gium. If it be wanting, its place is marked between the upper 

 quartzo-schistous system and the upper calcareous system. If 

 it exist, we must consider it as an extraordinary develop- 

 ment of the upper psammitic part of the quartzo-schistous 

 system. 



The English divisions established by Mr. Murchison are 

 founded upon the existence of fossils which appear to be dif- 

 ferent in each of them, and are consequently very proper to 

 characterize them. But these divisions, which are very good 

 for England, must present palaeontological differences more 

 or less remarkable in other countries, and this is in fact what 

 takes place in Belgium. We shall draw the attention of the 

 Academy to this at a future period. 



The Academy will moreover learn with pleasure, that 

 we have also recognised our four anthraxiferous systems in 

 the ancient tracts of the Boulonnais. In fact, if we direct 

 our course from the coal district of Ferques towards Land- 

 rethun, we see the following rocks appear successively, dipping 

 under the coal formation : 



1. Limestone. S. Dolomite. 



2. Dolomite. 6. Limestone. 



3. Yellow psammite. 7. Schist and red psammite. 



4. Limestone (Steinkalk). 8. Grayish schist. 



The limestone and the dolomite, Nos. 1 and 2, belong to the 

 upper calcareous system, the fossils of which moreover it con- 

 tains. 



The psammite. No. 3, has the characters and the position 

 of the upper quartzo-schistous system. 



The limestone and the dolomite, Nos. 4, 5 and 6, repre- 

 sent the three divisions of the lower calcareous system, and 

 contain the fossils characteristic of it ; for example, the Cya- 

 thophijllum quadrigeminim^ the Calamopora polymorpha, the 

 Terebratula concentrica^ some Spiriferae and Euomphali, &c. 



