PORTLAND ROCKS OF ENGLAND. 191 



bed in Portland ; Sowerhya DuJcei, and Buccinum naticoides appear 

 also to be peculiar, though infinitely more rare. 



The Trigonia gibhosa^, Lucina portlandica, Pecten lamellosus , 

 Ostrea expaiisa, and Natica elegans, it retains from earlier times ; 

 but Gardium dissimile appears to have died out. 



No. 2 is the " AYhit bed," whose qualities have made the island so 

 famous. The difference in its thickness in the different quarries has 

 long been noticed, especially its increase towards the west. The 

 fact is, it may be seen dying out, and very false-bedded if traced 

 beyond the quarries to the east. It is not properly oolitic, and 

 contains very few fossils. The true Ammonites gigantcus appears, 

 however, to be peculiar to it, those so called from other beds belong- 

 ing to distinct species. These uppermost beds are thus proved 

 local, even in the Island of Portland itself. The fact that they do 

 not occur elsewhere on the coast or at TJpway in the same character, 

 while the Purbecks remain similar, indicates some slight amount of 

 unconformity between the two series. The Roach and Whit bed 

 are also, it would seem, separated by unconformity, or at least con- 

 temporaneous erosion, from the beds below, and thus constitute a 

 stage in the ex^isode of a very marked character. 



Nos. 3-9 may be characterized as the flinty series. ISTo. 3 is the 

 " Curf," which varies in inverse proportion to the Whit bed, as 

 though the erosion of one had formed the basin for the other. It is 

 also oolitic, and contains, according to Damon, abundant Ostrea 

 solitaria, 



No. 4 is the " base "-bed, which, though very Hke the Whit bed 

 in appearance, is distinguishable from it by the presence of strong 

 irregular bands of flint. This and No. 3 are the home of the rare 

 Isastrcea oblonga and its perforating Litliodomi. The rarity of 

 corals may account for the scarcity of oolitic rocks. 



No. 5 and those below cease to have workmen's names applied, as 

 they are not quarried. The upper block is full of Trigonia gihbosa, 

 and may be named the Tingonia-hed. It is of so changing a thick- 

 ness as to suggest its being deposited on an uneven surface. In one 

 place it is seen lying on No. 6, and is not more than from 4 to 6 feet 

 in thickness ; whilst in the great cutting of the Verne Fort, further 

 to the north, it cuts irregularly into No. 8 and reaches nearly 20 feet. 

 At this spot it has been compared by Damon to the Eoach, from 

 which, as he remarks, it may be distinguished by the change of 

 fossils, Perna mytiloides taking the place of CeritJiium portlandicum. 



No. 6 is a remarkable mass about 3 feet in thickness. The upper 

 part is solid flint; but the lower part is a rubble-bed, made of broken 

 masses of limestone like the beds below, with a siliceous cement. 

 Here is another evidence of the irregularity with which the final 

 changes took place, which warns us that Nos. 3 to 5 may represent 

 another local deposit. 



No. 7 requires distinction, though essentially part of No. 8, be- 



* I cannot appreciate the diflferences which have led Messrs. De Loriol and 

 Lycett to establish a new species (?) T. Bamoniana for these ; the varieties pass 

 indefinitely into each other. 



