PORTLAND ROCKS OF ENGLAND. 199 



The topmost bed, Xo. 1, is a solid block, of a thickness of 3 feet 

 6 inches. The upper foot is a creamy limestone, not at all oolitic ; the 

 next foot is a shell-bed, full of Trigonice, but with no Cerithium port- 

 landicum; and the rest is a suboolitic limestone with few shells. 

 The identity of this with the uppermost three beds at Worth, which 

 are there 19 feet thick, is very obvious. The upper portion is cited 

 by Damon as belonging to the Purbeck, and quoted to show the 

 amalgamation of the two deposits. I have seen no proof of its being 

 Purbeck; and the corresponding bed at "Worth is full of Tri- 

 gonice. 



j^o. 2 is chalk and flint, the latter in large masses, and most 

 abundant towards the middle ; the chalk, however, is good enough 

 to burn for lime. The total thickness is about 40 feet. This is 

 said to be succeeded by 



jS'o. 3, a hard clay. There can be as little doubt that No. 3 cor- 

 responds to the clay at Portland which underlies the flinty series to 

 which jSTo. 2 here corresponds. As this in the same way corresponds 

 to Xo. 10 at St. Alban's, there must be 48 feet of rock, including the 

 quarried stone at Worth that is here absent. We may regard this 

 as a proof that the topmost beds, both here and at Worth, do repre- 

 sent the building- stones in different areas, and that the unconfor- 

 mity between them and the flinty series is a well-marked one. The 

 smaller amount of siliceous material in this locality apparently 

 encouraged vertebrates to frequent it, since the remains of Pycnodus, 

 Glihncera, and Turtle were obtained at one visit. The ordinary 

 fossils are those of the flinty series, e. g. Cardium dissimile, Pecten 

 lamellosus, Trigonia gibhosa, Lucina jportlandica, and Ammonites 

 holoniensis. 



I have not been able to visit Gorton, where the Portland sand is 

 said to be exposed and to yield Belemnites. In Pdngstead Bay this 

 part of the series is intermediate in development between that at 

 Portland and that at St. Alban's. Por the upper bed is 14 feet of the 

 sandy cement-stone, the clay having died out ; it is succeeded by a 

 3-feet lumachelle, as in Portland, and, finally, the hardened sandy 

 marl ad libitum, containing the same undulate Trigonia as at Port- 

 land, and another like T. gibbosa. 



The changes in the Portland series thus demonstrated in its typical 

 locality prove its essentially episodal character. Tho two most con- 

 stant portions are the lower part of the flinty bed and the sandy 

 cement-stones. 



4. The Vale of Wardour. 



Although the common fossils and the whiteness of the limestone 

 tell the geologist at once that the rocks of this district are Portland, 

 he soon finds, on coming to details, that they require study before 

 their relations to those of the typical district are made out. The 

 succession of the beds must be traced in various quarries ; but a 

 general account will be given of the whole. 



In the Museum of Practical Geology is a large block of stone from 



