AUSTEN ON THE BOULONNAIS. 237 



Bdis des Roches, where at one time they were worked for coal. In 

 the Bois des Roches, the whole carboniferous series is highly inclined, 

 the basset edges of the limestones projecting in great weathered 

 masses ; and thoxigh, from the thick growth of wood, it is difficult to 

 get at the structure of the mass, it is evident near the old shaft of 

 Autruit that the coal-measures are in an intermediate position : at no 

 other place do we find so great a thickness of the upper limestone. 

 As the sandstones of this place have been confounded by M. Rozet 

 with some others of a very different age, it may be as well to state 

 that these contain numerous impressions of Calamites and Ferns which 

 the sands above the Fiennes limestone do not. 



The high road due E. from Marquise is along a platform of oolite 

 which is of inconsiderable thickness. A well sunk at the back of the 

 great iron-works at Bouquinghen, reached Sandstones and shales with 

 impressions of plants, belonging probably to the coal-measures. 

 Further on the oolite is seen resting on limestone as at Rinxent. At 

 the turn off by Le Gentrie to Wiove, there is a slight descent into a 

 valley, which runs S.W. N.E., and which, from the dip of the ooUte 

 beds in the plateau, is clearly a valley of fracture ; in this are two 

 low rounded hills of coal-measure shales and sandstones ; these beds 

 overlie the Haut-banc limestone, which extends from the Chateau des 

 Barreaux to beyond the road to Hardinghen. 



I would also refer to this series the group of strata which attracted 

 the attention of the geologists of the Boulogne Meeting, and is to be 

 seen on the ascent to Hedriquand from the river : the local mining 

 engineers were disposed to place it above the Haut-banc limestone, 

 whilst the palaeontologists present affirmed that the fossils were cha- 

 racteristically Silurian. The group is exposed for a thickness of 

 80 feet, and consists of alternations of dark shales with bands of 

 greenish sandstone, surmounted by shales only, and as such corre- 

 sponds exactly with the lowest portion of the Hardinghen coal group. 

 The sandstone bands contain casts of Productce in abundance, and it 

 must therefore be considered as the extension of the baud of LeU- 

 linghen and Ferques. The relation of this group to the limestone 

 exposed in the sides of the valley, rather lower down, is clear : when 

 first seen at the level of the stream on the side towards Basse Nor- 

 mandie, it has a N.E. dip, which carries it beneath the shales and 

 sandstones, and the reasons for considering this limestone to belong 

 to the lower or Haut-banc group have already been given. 



The vertical thickness of the several component parts of the coal- 

 measure series is not uniform even on the limited area here described ; 

 the sandstone bands thin out amidst the shales ; lenticular seams of 

 pure limestone also are intercalated with the lower portion, and the 

 coal-beds have been found to thin out. The Hardinghen works would 

 show that there were about five distinct levels at which the formation 

 of coal took place ; the associated shales contain in abundance the 

 remains of Ferns, showing that the vegetation was terrestrial, whilst 

 the intervening sedimentary beds indicate the conditions met with in 

 |)ays and other protected portions of a sea-board ; and we may hence 

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