!>84 Rev. W. D. Covi/beare on a Geological Map of [April, 



bottom of this cliff' is found a coarse limestone of a brown 

 colour, full of cornua ammonis, turbinated univalves, &c. 



These alternations of argillaceous and calcareous beds con- 

 tinue to extend into the interior towards the east of Boulogne. 

 In a deep pit sunk at Souverain Moulin, about five miles from 

 the town in that direction, in a fruitless attempt to procure coal, 

 the workmen passed through 12 such alternations, and then 

 pierced a solid calcareous rock 100 feet in thickness, containing 

 ammonites. Below this, occurred a thin seam of wood coal, 

 and then 20 feet of a shelly limestone full of turbinated uni- 

 valves, small oysters, serpulee, &c. together with impressions of 

 ferns and other vegetables ; and, lastly, another thin seam of 

 carbonized wood, resting on coarse limestone. 



The coral rag is exhibited with well-marked characters about 

 nine miles south-east of Boulogne, near Samers, and the great 

 oolite may be seen in the country round Marquise at the same 

 distance on the north-east. Both these points approach very 

 closely to the chalk escarpment; so that if the green sand, iron 

 sand, &c. exist at all in these directions, they must be greatly 

 reduced in extent. 



Near Marquise, the oolite comes in contact even with the 

 older rocks of the coal formation, which show themselves in this 

 corner of the denudation almost immediately beneath the chalk. 

 This coal district presents a band of mountain limestone 

 accompanied by another of regular coal-measures. The princi- 

 pal marble quarries are at Ferques, and the principal coal mines 

 at Hardingen. The stratification is extremely confused and 

 contorted. 



2. Within the interior area of the basin of Paris, there is also 

 a small denudation exposing the oolites, in a district called the 

 Pays de Bray, a little north-west of Beauvais. 



3. Surrounding the Chalk and Green Hand of the Paris Basin. 

 — This series also may be seen emerging from beneath the 

 chalk in the coast westwards from the mouth of the Seine, 

 where they have been traced by M. de la Beche. 



Along the mouth of the Seine, on both sides, the chalk and 

 green sand repose on a blue marl and marl-stone. At Trouville 

 sur Mer, the oolites of the upper and middle formation, i.e. the 

 Portland stone and coral rag, emerge from beneath this marl. 

 Between Villers sur Mer and Dives, the clay separating the 

 second and third system (the Oxford clay) forms the base of 

 the cliffs, which are. capped by the lower beds of the coral rag, 

 and an overlying mass of green sand. Still further west by St. 

 Comme, Arromarehe, St. Honorine, Virrcville, and Grandcamp, 

 the cliffs present the inferior oolite resting on lias. 



Hence, a zone of these formations extends circling round the 

 chalky and arenaceous border of the basin of Paris, by Caen, 

 Alen^on, Poitiers, Bourges, Auxerre, Bar le Due, and Mczieres, 

 the oolites stretching beyond all these places, succeeded at a 



