425 



the fossils of this kind njentioned by Dr. Woodward, and others, 

 will show that very few indeed of this numerous species can now 

 obtain any other denomination than that of fossilia incognita; bo- 

 tanists not having yet been able to discover any existing analogous 

 plants. Plate III. Fig. 3, represents a fossil of this description from 

 Chepstow, in Monmouthshire. This, as well as most others of this 

 kind, is little more than an impression, covered with a bituminous film, 

 of a very inconsiderable thickness, its internal part being entirely 

 sand-stone. The explanation of this circumstance does not, how- 

 ever, appear very difficult. The plant, having been surrounded by 

 the soft, or fluid, materials, of which the sand-stone has been since 

 formed, its internal succulent part would soon waste away, and its 

 place be filled with the soft magma; whilst the more solid and lig- 

 neous epidermis would remain, and, after a time, would give its 

 correct impression to the surrounding lapidifying matter. Then 

 passing through the bituminous change, it would fill its own mould 

 with its own altered substance, forming such a surface, as the sur- 

 rounding stony matter would adhere to but slightly ; and would 

 therefore dispose to that separation, by which its form is displayed. 

 This fossil is frequently found, where strata of sand-stone are 

 found nigh to the strata of coal, in various parts of England and 

 of Wales. Mr. Martin says he has seen single joints of this fossil 

 in iron-stone; and one in particular, of a large size, measuring 

 about twelve inches in circumference. Mr. Da Costa relates, that 

 in the collieries at Swanwich, in Derbyshire, in 1752, a plant of the 

 cane kind was found, fourteen feet long : it ended in a point at one 

 end, and at the root in a large knot ; and in the middle measured 

 nine inches about*. He also mentions, that Dr. Woodward describes 

 two specimens of this kind ; one a yard long, and the other six feet 

 and a half in length. Reference to Dr. Woodward's Catalogue 



* Philosophical Transactions, Vol. L. Part I. p. 2S1. 

 VOL.. I. 3 I 



