234 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Owing to the surface accumulations, tlie lower limit of this second 

 limestone group is not very clearly defined about Malassise ; yet the 

 superficial breadth and the high angle to be obserred throughout 

 show that the three groups here described form a series of consider- 

 able vertical dimensions. 



A little to the south of the line above noticed, another section may 

 be taken across the same series. At the westernmost of what are 

 known as the Napoleon Quarries, near Blecquenecque, where the road 

 crosses the line of an occasional watercourse, the beds of limestone 

 are seen to dip E.N.E., but are much fractured. At a second quarry 

 they dip E., subsequently they present a mere undulation, and finally, 

 where they emerge clear of the Great Oolite, they slope rapidly to the 

 S.W., the basset edges semng to mark the strike of the beds very 

 distinctly. 



The old coal-works of Ferques, which were established on the out- 

 crop of the coal-seams, are immediately on the N.E. of these lime- 

 stones, and, as in the former section, the coal-measure group is 

 succeeded by the lower limestones, having a S.W. dip of 30°. In 

 this section the outcrop of the coal-measures between the upper and 

 lower limestones is more distinct than in the other, and it is also 

 shown that the Napoleon marble is a subordinate band in the upj)er 

 limestone. 



It is clear from these two sections that the coal-measures of Ferques 

 and Leulinghen are intermediate between two great limestone groups, 

 to which they form a very natural systematic division. M. du Souich 

 gives the true position of the Boulogne coal in several passages of his 

 memoir *, yet I found that his views had not been readily adopted 

 even bv mining engineers, and that some were disposed to consider it 

 as occupying a great fault or fissure. The main fact in favour of this 

 view is the high angle of the coal-seams, which is alleged to be greater 

 than that of the limestones, a consideration to which the practical 

 geologist will not attach much importance : wherever thick masses of 

 strata variously composed have been much disturbed, the more yield- 

 ing beds, such as clays and shales, invariably show a greater amount 

 of dislocation than the thick compact masses which may include thenl ; 

 and such is the case in this instance. 



The lower limestone group may be followed from La Coste by Bois 

 Sergeant, Ferques to Elinghen, where, as N.E. of the church and in a 

 large quarry overlooking the stream, it dips to the S.W. The stream 

 here runs along a line of fault, on the west of which there is an upcast 

 of the limestones : the inclination of the beds veers round to N. and 

 E.N.E., and they rise gradually till at Haut-banc the limestone attains 

 an elevation of 280 feet. 



The upper or " little quarries " at Haut-banc consist of thin-bedded 

 limestone and of sandy magnesian limestones : in this portion a spe- 

 cies of Lithostrotion is very abundant. The great quarries present a 

 vertical thickness of 60 feet, consisting of beds which underlie the 

 above. This portion has an upper series of thin strata with occasional 



* Sur la Course Geologique du 11 Sept. 1839 ; Bull, de la Soc. Geol. de Fr. t. x. 



