PORTLAND ROCKa OF ENGLAND. 201 



Nevertheless they occupy the same position in the series, and IS'ature 

 must have repeated herself in independent areas. Unfortunately 

 the thickness of this mass and its relations to the bed below cannot 

 be accurately ascertained, as the junction is covered in the only 

 quarry in which I have seen this part of the formation. It may be 

 16 feet. 



No. 3. White chalk, like that of Upway, having abundance of 

 flints, both in beds and in fissures, throughout the upper 14 feet, 

 but none in the lower 12 feet. This is sufiiciently pure to burn for 

 lime; towards the base, however, it becomes harder and more 

 shaly. It is remarkable for the abundance of its common Portland 

 fossils, such as Pecten lamellosus, Cardiurru, dissimile, Lucina port- 

 landica, Pleuromya telHna, and Ostrea expansa. It has also many 

 Trigonice, both 2\ gihhosa and clavellate ones, and a few rarer fossils. 



No. 4 consists of two parts, which vary rapidly; the upper part 

 is a solid block of about 2 feet to 4 feet, with few fossils except 

 Trigonice-, the lower is a softish limestone, crowded with fossils, 

 and making up a total of 8 feet. This is one of the most fossili- 

 ferous beds of the formation ; and the fossils are beautifully preserved 

 as calcite. The most common is Astarte rugosa, every fragment 

 containing it. Associated with this is Cerifhium concavum, which 

 appears really to differ from C. portlandicum^ and to be found in 

 this bed to the exclusion of the latter. There is also C. Bouchar- 

 dianum, Nerita transversa^ var. minor, with its colour-spots, and 

 Neritoma sinuosa in great abundance. 



No. 5 is a Trigonia-hed, scarcely separable from the beds below, 

 and varying from zero to about 4 feet. The species is T. gihhosa 

 as usual. 



No. 6 is the great mass of stone for which aU the quarries in the 

 neighbourhood are worked. It is a fine freestone, more or less false- 

 bedded, and consisting of great blocks in fairly thick beds, but in 

 places somewhat concretionary. It is more of a sandstone than a 

 limestone, though somewhat calcareous. Here and there in some 

 quarries are thin bands of flint, in others bands of Trigonice pre- 

 served in chalcedony. According to Pitton, a similar chalcedonic 

 band has yielded the Isastrcea ohlonga. Large Ammonites holoniensis 

 are found here, and A. hiplex. The total thickness of this has not 

 been ascertained ; the greatest amount seen is 17 feet ; and this is 

 certainly not far off the maximum. 



No. 7. In one valley, about two miles W. of Tisbury, the stone 

 No. 6 was traced down the slope by surface-fragments from the 

 Astarte rw(/osa-bed at the top to an outstanding mass of a Trigonia- 

 bed, which is thus proved to underlie the stone ; but of its thickness 

 or arrangement no particulars could be ascertained. 



These form the only rocks which would by any one be referred to 

 the Portland Stone. As far as No. 3 they agree fairly with the 

 Upway beds, and so with part of the flinty series of Portland. The 

 fossiliferous zone below is not met with in the same form to the 

 south, though its most abundant fossils are found in Portland, and 

 probably in the flinty scries. The lower bed (No. 6), which is 



Q. J. G. !S. No. 142. p 



