and Silurian Systems in Belgium. 149 



I ought however to observe, that we also found there Pro- 

 ductus, and other shells which are generally met with in tiie 

 upper calcareous system. 



The schist and the red psammite, No. 7, occupy the position 

 of the lower quartzo-schistous system, of which it has more- 

 over all the mineralogical characters. 



Lastly, the grayish schist, No. 8, may be considered as 

 belonging to the upper part of the slate district. 



Such are the approximations which my foreign journeys 

 have enabled me to make; we will now review the observa- 

 tions I have made in our own country. 



I commenced by determining the boundaries of the slate 

 and anthraxiferous districts of Brabant, and of the northern 

 part of the province of Hainault, which led me to ascertain 

 that at the farm of Hongree, near Ronquieres, the conglome- 

 rates, the schist, and the red psammites of the lower quartzo- 

 schistous system repose in unconformable stratification upon 

 the truncated beds of the slate formation. Now it is to be 

 remarked, that in the north of Belgium the upper slate sy- 

 stem is generally very little developed or entirely wanting, 

 which explains this fact which is contrary to what I have 

 hitherto observed on the northern edge of the Ardennes, 

 where the slate and anthraxiferous formations are not merely 

 stratified in a perfectly conformable manner, but also pass so 

 insensibly from one to the other, that it is impossible to trace 

 a line of demarcation between the two formations. 



I also discovered several undescribed beds of porphyry, 

 namely, at a quarter of a league north of Henamyeres, to the 

 south of Audimont, to the south and south-west of Fauque, 

 in the road from Monstreux to Grand Abay, and near the road 

 from Monstreux to Nivelles. These beds hardly deviate 

 from a straight line drawn from Enghien to Nivelles. 



The porphyries vary in texture, and have produced some 

 slight alterations in the schistose rocks near Monstreux, which 

 will be noticed in detail, when we have examined the slate 

 formation of the north of Belgium in all its extent. 



I afterwards paid particular attention to the tertiary and 

 modern chalk formations. I have made a great many excur- 

 sions in the provinces of Flanders, Antwerp, and Limburg, 

 in order to have a complete idea of the different modifications 

 which they present; and I have thus laid down the outlines 

 of operations, the details of which only remain to be filled up. 

 To the latter also I have already applied myself in the district 

 of Fauquemont (a province of Limburg), and I hope that 

 the five northern provinces of Belgium will be finished next 

 year. The district of Fauquemont is one of the' most inter- 



