AUSTEN ON THE BOTJLONNAIS. 239 



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v«n! <; Second Division. M&ilai s-xq i 



Yellow Sandstone G?-oup. 



1 . A band of shale, but of which it is difficult to ascertain the 

 thickness, may be seen next beneath the mountain- hmestone-dolo- 

 mite, near Le Hure, as also about Ferques. I was unable to observe 

 any break of continuity with the beds above ; it would seem as if the 

 progress of accumulation passed uninteruptedly on, changing gradu- 

 ally from argillaceous mud to calcareous mud, yet so as to make it 

 impossible to draw any natural divisional line ; yet some such line is 

 rendered necessary from the change of animal forms, which becomes 

 very marked at about this part of the series. 



2. As far as my own observations went, this band of argillaceous 

 shale is non-fossiliferous, but immediately beneath it is a group of 

 strata characterized by a subordinate band of sandstones, which may be 

 seen in the road-section from Landrethun to Ferques ; at this place 

 bands from a few inches to a foot in thickness are I'epeated at wide 

 intervals, and so pass into the shale band placed at the head of this 

 division. In this section the superficial breadth of the sandstone 

 series is 22 yards, with a S.W. dip of 20°, which gives a thickness of 

 about 25 feet. 



This sandstone is again seen in a lane-section E. of Ferques, as 

 also on the left of Beaulieu stream, opposite Le Hure ; thence it 

 crosses the Bois de Beaulieu, and runs out on the Crembreux stream, 

 where its whole thickness is exhibited in a large quarry. The sequence 

 of the beds is just such as at Ferques. 



This sandstone is fine-grained and exceedingly micaceous ; it is of 

 a beautiful clear yellow, occasionally in the lower seams acquiring a 

 faint red tinge ; it is used for a variety of purposes, such as for floor- 

 paving, feeding-troughs and window- mullions. The surfaces of the 

 partings of the beds present beautiful impressions of Fucoids. 



This sandstone is the Gres a Unio of M. Rozet, from a supposed 

 resemblance of a shell it contains with the Utiio subconstrictus of 

 Sowerby ; he considered it to be of the same age as the Millstone grit 

 of the English coal-measure series ; it was the Psammite de Ludlow 

 of the Boulogne Meeting. It has been confounded with the sand- 

 stones of the coal-measures, as by MM. Dufrenoy and Elie de Beau- 

 mont (Explication de la Carte Geol. de France, vol. i. p. 783). 



The fossil remains occur only in the condition of casts, but we 

 were enabled to procure such specimens as leave no doubt as to the 

 species to which they are referable ; they are — Cucullcea Hardingii, 

 C. trapezium, C. 1 amygdalina. There are two species of Cypricar- 

 dia, and a Bellerophon, which has been quoted as B. bilobatus. 



The forms of Cucidlaa here noticed are of much interest, inas- 

 much as, together with the Cypricardia, they occur in a very similar 

 sandstone in the Devonshire series of Baggy Point and Marwood, 

 and range downwards from that zone, wherever sands occur, as low 

 as the Ilfracombe group ; they thus enable us to place this portion of 

 the Boulogne series in correspondence with our own. 



