Mr. Webster on the Purbeck and Portland Beds. 43 



found in convenient situations. Beneath this^ the quality of the rock changes 

 considerably; it becomes more varied in its texture/ and is much mixed with 

 chert. Some parts of it are not oolitic, but grey, and of a splintery fracture ; 

 other parts are brownish and slightly oolitic; while others again are very 

 soft and white, and contain bodies resembling parts of coleopterous insects. 

 This last portion was within 18 inches of the Kimmeridge beds. It is rather to 

 the lower, than to the upper bed, of the good stone of Portland, that I refer 

 the Purbeck Portland, which is generally but slightly oolitic, and contains 

 much calcareous spar : this renders it a harder stone, and fitter for many 

 purposes of building where durability is required. I should state that with 

 the Purbeck Portland is also found another stone not at all oolitic, but gra- 

 nular, and resembling exactly the stone of Caen in Normandy, which, it is 

 well known, was formerly imported into this country, and much employed in 

 sculpture. 



I examined also several other quarries at the north end of the Island, where 

 the same beds, and nearly in the same proportion, could be distinguished : but 

 on the south-east side, where quarries are also worked, the beds differ consi- 

 derably in their subdivisions. The Slate and Cap occur, but not the lignite ; 

 and the Roach, though still considerable, was subdivided into 3 beds ; below 

 which the chert was in greater quantity than on the north side. At the south 

 end of the island, from the dip being to the south, the top of the series came 

 within about 20 or 30 feet of the sea, and the lower beds were invisible. 

 There are no quarries in this part. 



Immediately below this great calcareous series, in the Isle of Portland, are 

 seen very thick beds of bituminous clay and bituminous limestone, resembling 

 those at Kimmeridge which I had before visited : but as it is not my object at 

 present to enter into the consideration of the Kimmeridge strata ; I shall only 

 now state that the identification of the beds at the base of Portland Island 

 and at Kimmeridge is, I conceive, as complete as such a subject admits of. 



Having now taken a rapid view of these two series, viz. the Purbeck and 

 Portland beds, which well deserve a still more particular examination, I cannot 

 help stating that there appears sufficient reason for keeping them separate from 

 each other in grouping the strata. Perhaps no distinction is more remarkable 

 than that depending upon the organic remains derived from fresh-water and 

 marine animals ; and although this subject, and the mode of recognising the 

 fossil remains, be extremely difficult and obscure, yet the facts I shall proceed 

 to state, added to so wide a variation in mineralogical character, may perhaps 

 justify my opinion. 



1 have in another place alluded to the analogy between the Purbeck beds 



g2 



