20 



Prof. BucRLAND and Mr. De la Beche on the 



concretions resembling the cow-stones in the lower green sand at these two 

 places ; its fossils^ however, are different, and more allied to those of the 

 oolite ; and its position beneath the Portland stone is decisive in separating 

 it totally from the greensand formation. We have adopted for this stratum 

 the name of Portland Sand, being that suggested by Dr. Pitton, who had 

 ascertained its relation in the Boulonnais and in Buckinghamshire*. 



This Portland sand is of sufficient importance to be marked on our map by 

 a distinct colour along nearly the whole extent of the base of all the escarp- 

 ments of Portland stone ; its mineralogical resemblance to the greensand of 

 Lyme may be best seen at Gorton, about two miles west of Upway, where 

 nearly one half of its substance is made up of grains of green earth. 



The following list of fossils from the Portland sand has been prepared by 

 Mr. James Sowerby, from specimens we collected at Black Nore and Chesil- 

 ton, in the Isle of Portland, and at Gorton. 



Black Nore. 



Serpula plexus, M. C. 598. f. 1. 



Mya? (Pullastra of Phillips), only a cast. 



Trigonia clavellata, M. C. 87. 



Plicatula, a new species, occurs at Weymouth. 



Pecten, with concentric laminae. 



Exogyra (Gnjphcea) nana, M. C. 383. f. 3. 



Ammonites triplex. M. C. 292, 293. 



Mya ? same as at Black Nore. 



Venus, only a cast. 



Ostrea Hemicyclus, new species. 



Ghesilton. 



Exogyra nana. 



Ammonites giganteusi young, M. C. 126. 



Gorton. 



Lucina? a fragment. 



Cardium, small fragment. 



Avicula concenirica, new species, very abun- 

 dant. 



Pinna viminea, new species ; found also at 

 Down Cliff, Bridport, in inferior oolite. 



Pecten, with concentric laminae. 



581. 



Plagiostoma rusticuml M. C. 



Ostrea, new ? 



Anomia ? one valve imperfect. 



Belemnites, fragment. 



Ammonites giganteusi Young, or possibly y^. 



Vernoni of Phillips : it is much crushed. 

 Echinus spines. 



The prevailing character of this stratum, along the whole line coloured on 

 the north side of our map, is a bed of siliceous sand and green earth. It is 

 also sandy and full of green earth at the village of Ghesil ; but at the base of 

 the high west cliff of Portland, under the promontory of Black Nore, where 

 it attains a thickness of eighty feetf, it is mixed with marl, and exhibits 

 subordinate concretions, and beds of sandy marl and sandstone, both contain- 

 ing the same fossils that are found at Ghesilton and Gorton. Its lowest beds 

 become more argillaceous as they approach nearer to the subjacent Kim- 



* See Phil. Mag. and Ann., May 1827, vol. i. p. 139. 



t See PI. III. fig. 1 & 3. 



