Geological Society. — Horticultural Society. 377 



pavements, &c. is derived. This stone is composed almost en- 

 tirely of fragments of shells ; the Purbeck marble contains 

 chiefly univalves in a compact limestone, and these in general 

 are smaller than the univalves of the Petworth marble, both 

 having been supposed to belong to freshwater shells ; but the 

 author possessing specimens that contain a mixture of marine 

 with fresh-water shells, he cannot consider this as a decided 

 fresh-water formation, a term that in his opinion ought to be 

 restricted to those beds supposed to have been formed in lakes 

 only. The common Purbeck stone appears to consist of frag- 

 ments chiefly of small bivalves of which the origin is doubtful. 



Mr. Webster then gave a detailed account of the quarries 

 of the Isle of Portland^ which furnish the Portland stone much 

 used in our public buildings. The Isle of Portland consists 

 of a calcareous mass lying upon a bed of bituminous clay and 

 limestone identical with the Kimmeridge beds. The lower and 

 more considerable part of the limestone in the Isle of Portland 

 above the Kimmeridge clay is chiefly oolitic, and contains 

 beds of chert; but the upper part consists of a yellowish cal- 

 careous stone nearly compact, which contains in it a bed of 

 earthy lignite, abounding in silicified portions of trunks of trees 

 about two or three feet long, some of which are erect, and 

 others are lying flat. As far as he could ascertain, the fossil 

 wood was nearly confined to this stratum, and not dispersed 

 through the oolite as had hitherto been supposed. These up- 

 per beds of the Isle of Portland, he considered as belonging 

 to the same formation as the Purbeck beds, having found some 

 very similar in the Isle of Purbeck. 



Considering the fossil shells of the Portland oolite to be ma- 

 rine, while those of the Purbeck limestone, are chiefly fresh- 

 water, together with the great mineralogical difference of cha- 

 racter, the author stated it as his opinion, that the two series 

 of beds should be kept in separate groups in arranging the 

 English strata. 



HORTICULTURAL SOCIETY. 



Sept. 7.— The large silver medal was presented to Robert 

 Austen of Glasgow, a Corresponding Member of theSociety, for 

 the successful cultivation of Scotch roses, many new varieties 

 of which have been raised by him, and presented to the gar- 

 den of the Society.— The large silver medal was also presented 

 to Peter Caesar Labonchepe, Esq., F.H.S., fur having intro- 

 duced and encouraged the Dutch method of early forcing.— 

 The large silver medal W8* also presented to Mr. Henry Burn, 

 gardener to the Marquis of Aylesbury, a Corresponding Mem- 

 bersol tin- Society, for having raised the seedling grape called 

 the Tottenham Park Muscat 



Vol. 64. No. ;n>. Nov. 1824. ■'* H 1 1"' 



