Yol. 52.] A DELIMITATION OF THE CENOMANIAN. 109 



Section at Lulworth Cove. 



Feet. 



/'Soft, greenish, buff-coloured marl (zone of Bel. plena) 6 



I White chalk in regular beds, divided by thin seams of marl 16 

 Lower Chalk. ■{ Soft, whitish chalk, blocky and not bedded, enclosing 



siliceous nodules or flints 12 



^ Glauconitic chalk with phosphatic nodules 4 



/^Hard, nodular, calcareous sandstone (1 foot), passing 

 down into similar but more sandy and evenly-bedded 



Zone of J rock ; many fossils 8 



Pecten asper. J Sand with two or more layers of chert 5 



I Marly greensand with small phosphatic nodules, Pecten 



\ asper and many other fossils 7 



f Greensand with beds of calcareous sandstone 14 



Greenish sand with an oyster-bed 10 feet down and a layer 



of fossiliferous concretions at the base 16 



Grey micaceous sands with two layers of grey sandstone : 



Vermicularia concava 44 



Black sandy clay, seen for . 15 



Dark blue clays (?) 45 



Zone op Am. 

 rostratus. 



Gault 



v. 



•I 



In this section a noteworthy point is the occurrence of flints in 

 the Lower Chalk. These flints do not disengage themselves like 

 ordinary chalk-flints, but have more resemblance to the siliceous 

 concretions which occur in the Lower Chalk of Wiltshire. 1 They 

 are enveloped in a thick coat of white siliceous chalk, which often 

 seems to pass inward into grey or black flint and outward into the 

 pure chalk. The amount of completely silicified matter or flint 

 varies greatly, being sometimes a fairly large mass and sometimes 

 a mere nucleus, and some concretions have none at all. 



These flints also occur at Whitenose and in many other parts of 

 West Dorset, and we call especial attention to them, both because 

 the idea that real flints do not occur in Lower Chalk is still current 

 in some quarters, and because siliceous concretions of the nature of 

 cherts occur in the Cenomanian of Normandy. 



Lithologically there is nothing at Lulworth which can be called 

 Chalk Marl, but, as Dr. Barrois records Ammonites varians and 

 Mhynchonella Mantelliana from these beds at Bingstead Bay, they 

 may represent part of the Chalk Marl. Whether the basement-bed 

 with its phosphate-nodules represents the true Chloritic Marl or 

 Stauronema-bed we think very doubtful ; more probably it should 

 be regarded as a condensed equivalent of the lower part of the 

 Chalk Marl. 



The junction of Chalk and Greensand is even more abrupt and 

 well marked than at Punfield, the base of the giauconitic chalk 

 resting on an uneven and current-washed surface of the underlying 

 sandstone. The uppermost foot of this sandstone, moreover, is 

 rough, nodular, and more calcified than the part below, as if it had 

 been exposed to some alterative influences before the deposition 

 of the overlying chalk. 



The zone of Pecten asper is well marked ; the chert-beds are 

 coming in again, and, with a marly greensand below, in which 

 Dr. Barrois also found P. asper, give the zone a thickness of 20 feet. 



1 See Quart. Journ. Geol. Soc. vol. xlv. (1889) p. 403. 



