Mr. Murchison on the Freshwater Beds of Brora. 73 



Instead of supposing that the oolitic series of the cliffs near Portree 

 was overlaid by a true equivalent of the Wealden*, the freshwater 

 beds of Skye will it is now believed be found, like those of Inver- 

 brora, to be interstratified with the middle oolite, a conclusion ren- 

 dered probable by the natural sections and form of the coast, and 

 by the circumstance that the fragments not found in situ which 

 contained freshwater shells were collected near the escarpment and 

 not on the dip of the oolitic strata. Mr. Murchison is inclined to 

 take a similar view of the freshwater deposits near Elgin, compared 

 by Mr. Malcolmson to the Purbeck beds of England. 



The author remarks, that with the terrestrial evidences in the plants 

 of Portland, Scarborough, Stonesfield and Brora, we might naturally 

 expect at any day to hear of the associated lacustrine or river shells. 

 But Mr. Robertson's discovery further compels us to believe, that the 

 same species of freshwater shells prevailed, not only during the whole 

 of the Wealden epoch, but that they were in existence at periods 

 long antecedent, when the adjacent lands poured forth rivers into the 

 sea in which the middle and lower oolites were accumulated, and 

 thus we acquire a new element to enable us to reason upon the 

 former conditions of the surface. 



The facts stated by Mr. Robertson tend to confirm the idea, that 

 the Wealden is more naturally connected with the Jurassic than 

 with the cretaceous system, and must also have an influence in de- 

 ciding that the Neocomian formation of foreign geologists ought not 

 to be placed on the parallel of the Wealden. Mr. Murchison has for 

 some years been of opinion that the Neocomian system is little more 

 than an equivalent of the lower greensand of British geologists, a 

 view which he upheld at the meeting of the Geological Society of 

 France at Boulogne in 1839, on the ground of the identity of their 

 stratigraphical relations and typical fossils. Further researches du- 

 ring last May along the coast of the Isle of Wight, in company with 

 Count Keyserling, led both that gentleman and the author to the 

 same conclusion. Among the numerous fossils they there collected 

 were many identical with, or analogous to, Neocomian species, par- 

 ticularly in that portion of the coast section so minutely described 

 by Dr. Fitton and Sir John Herschel, viz. between Black Gang 

 Chine and Atherfield rocks. Mr. Murchison observed that there 

 seemed to be a gradual zoological as well as lithological passage from 

 the Wealden beds below into the greensand and shales above them ; 

 for although the shale with Cypris occurs immediately beneath the 

 marine deposit of Atherfield rocks, as remarked by Dr. Fitton, 

 another band of flagstone with marine shells (Ostrea and Terebra- 

 tula) also occurs beneath these uppermost beds of Cypris. In the 

 still lower strata, however, we lose all traces of such marine alter- 

 nations, and the whole becomes one great freshwater deposit. A 

 similar phsenomenon is seen in the southern part of the section at 

 Red Cliff, extending into Sandown Bay, where beds with Cypris are 

 intercalated between oyster beds. These alternations are indeed 

 what we might expect to find, provided a former depression of the 

 * Geol. Trans, vol. ii. p. 366. 



