232 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



in 1840, in which there will be found a theoretical section and a new 

 systematic division of the Boulogne Palaeozoic series into Carbonife- 

 rous, Devonian, and Silurian. 



More recently M. Delanoue * has proposed to arrange the Boulon- 

 nais series according to M. Dumont's Belgian system: the lowest 

 beds of this locality are identified with the "Terrain Rhenan," and 

 which is considered to be " Silurian." 



§ 1 . Sequence of the Palceozoic Rocks of the Boulonnais in 

 descending order. 



First Division. 



Limestones above and below the Coal. — At a spot where the high 

 road from Marquise to Calais crosses the Blacourt stream, a con- 

 siderable mass of Great Oolite is seen resting on a dark thick-bedded 

 crystalline limestone ; below the bridge the beds are nearly horizontal ; 

 they can be traced along the course of the stream upwards, but 

 beneath the hamlet of Leulinghen, and on the right bank of the 

 stream, the limestone has a dip of 25° N.E. ; the lower thick beds 

 are here surmounted by thin and fragmentary ones. Across the 

 stream, and on the ascent to the farm of La Coste, like beds are 

 surmounted by the lowest stratum of the oolite, containing numerous 

 small Ostrece. A little above this the table-land again presents a bare 

 limestone surface, over which are several quarries and the spoil of the 

 old coal-works of Leulinghen. The southernmost portion of this 

 limestone may be seen in two places to dip 25° S. 



This limestone is succeeded on the surface by a band of shales and 

 sandstones, and subordinate to which are the seams on which the old 

 coal-works of Leulinghen were established. The strike of the outcrop 

 of these coal-measures corresponds with that of the limestone imme- 

 diately adjacent. The works are now abandoned, but I was informed, 

 by one who was well acquainted with the mines, that the beds sloped 

 away at a high angle to the south and were much disturbed. The 

 breadth of the outcrop of the coal-measure series is not more than 

 100 feet. 



Immediately to the north of the coal-measure band there is an ex- 

 tensive tabular surface of hmestone, of which the east and west strike 

 is well-defined, the dip being south : these limestones therefore un- 

 derlie the coal-measures. These lower limestones extend northerly 

 and easterly towards La Malassise and Bois Sergeant ; in these direc- 

 tions they are overlaid by thick accumulations of gravel-sand, brick- 

 earth, and pipe-clay, with much vegetable matter, and which have to 

 be worked through for the iron-ore beneath f. These limestones are 

 much fractured, but dip invariably to the south on the side towards 

 La Coste, and to the south-west about Bois Sergeant ; this change of 

 strike is caused by a fault which is clearly indicated on the present 

 surface : the dip is variable, being never less than 30°, and in places 

 as much as 42°. 



* Bull. Soc. Geol. de Fr. 1853. 



t The whole of this series of accumulations in the Boulonnais is peculiarly de- 

 serving of attention. 



