75^ Geology of the Shore of the Severn. 



3. A shell (see the annexed figure) which was discovered by Mr. R. 

 Ryder, of Awre, (see note, p. 70,) and which I have, therefore, named 



-half inch, the smallest spe- 

 1 l-5th inch, the largest-sized ^ clmen hitherto found. 



Byderia hitherto found. 



Shewing the hinges of (a). 



Rydei-ia. Respecting this shell, the late Mr. Parkinson, author of the 

 " Organic Remains of a Former World, &c.," writes thus to Mr. Ryder. 

 ** It is curious, that amongst those fossils with which you favoured 

 me, there is not a single separated valve, by which, of course, I am 

 prevented determining the genus ; but which, I believe, is new. They 

 are very interesting indeed, from their long, and even fistular termi- 

 nations.'' Only one single valve of this shell has hitherto been found. 

 This was only a very minute one, and broke to pieces immediately, on 

 being touched. The only locality of this fossil is at the point i, or the 

 Woodend. 



4. Specimens of a sort of carbonized wood, much resembling Bovey Coal ; 

 in which occurred, traversing its fractures in small lamellar pieces, a 

 white substance, not hitherto met with in that matrix, and which, on 

 examination by Mr. Brande, proved to be sulphate of barytes. This 

 was found near the point i. 



5. The petrified trunk of a tree, fourteen feet long, not far distant from 

 the locality of No. 4, traversed by veins of sulphate of barytes, pre- 

 senting a form exactly similar to that of the coal of No. 4. Upon this 

 mineral, Mr. Brande, in writing to me, observes : ♦• The veins in the 

 petrified wood, of which I duly received the specimens from Mr. 

 Powell*, are, as you very reasonably anticipate, sulphate of barytes. It 

 is an interesting fact, that the same substance should be found travers- 

 ing both the wood and coal." 



From the preceding memoir, it is worthy of observation, that 

 we find three periods distinctly marked out, in which the same 

 species of animals have existed alive on the earth, and pro- 

 bably not far from the spot where their remains are found, 

 mz., prior to the Deluge; at the time of the formation of the 

 alluvial deposition ; and during some portion of the period 



* My very good and particular friend, the Savilian Professor of Geometry at 

 Oxford, •' 



