272 M. RE Bonnarb's Notices 



but that the granitic porphyry knolls, which are isolated in 

 the midst of the schistose rocks of Hainault, occur at a very 

 short distance from the line which would join these two 

 granitic points.* 



Without pretending to draw from this fact, considered 

 alone, conclusions which would at least be very hazardous, 

 I conceive that it may be regarded as supporting the facts 

 which lead us to doubt the primordial nature of the granite 

 and the other crystalline rocks of the Hartz, and as making it 

 presumable tliat this country offers another example of the 

 return of the most crystalline ancient rocks in the midst of 

 transition formations. 



The transition rocks of the Hartz, at least those generally 

 recognised as such, considered alone, present among them- 

 selves relations conformable to those elsewhere observed in 

 similar formations. The general dip of the beds to the 

 S. S. E. leads us to suppose that the more ancient parts of the 

 schist and greywacke formation should occur at the northern 

 limit of the group, and there, in fact, we observe either a 

 characterised clay slate, long regarded as primitive, and 

 which very rarely contains some scarcely determinable re- 

 mains of marine animals, or a greywacke of such a fine and 

 close grain, that its arenaceous structure is with difficulty 

 distinguishable. Advancing towards the S. and S.E., i.e. 

 on beds resting on the preceding, the schists become less 

 fissile, more dull, more micaceous, more shelly, sometimes 

 contain small rounded grains, and thus pass into greywacke; 

 this last becomes visibly arenaceous, and the rolled frag- 

 ments it contains, increase in bulk so as to acquire the 

 size of the head ; it moreover contains numerous remains of 

 plants, the surface of which is penetrated by anthracite, and 

 entire sandy and often slightly calcareous beds (psammites 

 sableux of M. Brongniart), filled with the shells usual in 

 this formation. 



The greywacke of the Ilartz contains, as Messrs. Lame 



* See Essay on the Geology of the North of France, by M. Omalius 

 d'Halloy. Journal des Mines, No. 142, p. 301, &c. 



