Geological Society. 139 



summit of the cliffs between Gris-nez and Equihen; where a thin 

 bed occurs of somewhat bituminous clay, abounding in silicified 

 wood, the cavities of which are coated with minute crystals of 

 quartz. This bed corresponds precisely to that which exists on 

 the top of the Isle of Portland, bearing there the name of ' Dirt,' 

 and abounding in similar wood; and on the French coast it is as- 

 sociated with beds of limestone, different from the stone beneath, 

 and containing shells in great numbers, apparently of the genera 

 Cyclas and Ampullaria. The next stratum of the Boulonnois is 

 the equivalent of that form of the Porlland limestone which occurs 

 at Garsington and Shotover Hill in Oxfordshire, and at Brill and 

 other places in the vicinity of Aylesbury in Buckingamshire: — 

 respecting its geological relations, however, some doubts still remain 

 to be cleared up ; several of the fossils being the same with those 

 of the Isle of Portland, but the aspect of some of the beds a good 

 deal different. The formation in the Boulonnois consists, as in 

 Oxfordshire, of calcareous concretions of great size, abounding 

 in petrifactions, and imbedded in yellov/ish somewhat ferruginous 

 sand: — and the appearances of the stratum, especially between 

 Gris-nez and Audresellcs, where the shore is covered with these 

 enormous masses fallen from the sands above, is exceedingly striking 

 and remarkable. To this formation a series of beds succeeds, the 

 equivalent of the strata between the Portland limestone and the 

 coral rag ; — corresponding precisely to those of the shore near Wey- 

 mouth, and consistTg of alternations of sand, limestone and clay, 

 in some instances bituminous and abounding in fossils. — These oc- 

 cupy the whole of the lower part of the clifis from Gris-nez to 

 Equihen, and are visible in several places in the interior. The 

 pisolite and coral rag are not seen upon the coast, but come up at 

 a short distance within it ; and their outcrop is conspicuous at Ba- 

 singhen, and along a line extending from that place, by Wierre and 

 Hautenbert, to Alinctun. On the north of that line this formation 

 is succeeded by a valley constituting a very remarkable feature of 

 the country, and occupied by beds of clay containing fossils iden- 

 tical with those of the Oxford clay, and including, especially at the 

 lower part, subordinate beds of sand and calcareous grit. These 

 are followed on the north, near iVIarquise, by the equivalent of 

 the Bath oolite., (the upper members of the oolitic series, Cornbrash 

 and Forest marble, being indistinct or wanting) : — and this for- 

 mation seems to come in without any intervention, immediately 

 after the gault or subjacent sand, on the north of the denudation ; 

 where it occupies the surface, in nearly horizontal strata |)laced 

 unconforniably over beds of the coal formation, or oi mountain lime- 

 stone. — The former of these is disclosed in a small space only, in the 

 vicinity of Hardinghen : and the author refers for an account of it 

 to a Memoir now preparing for publication by M. Garnier of Arras. 

 — The mountain limestone, which is the lowest formation of ihe 

 Boulonnois, in some places conies in immediately after the lower 

 greensand, or the gault, without the intervention even of the oolite: 

 and near Landrethun the distance from the chalk to the limestone 

 beds is not more than a quarter of a mile. In some cases, when 



T '1 the 



