1845.] MANTELL ON THE WEALDEN OF THE ISLE OF WIGHT. 93 



feet in diameter. I traced two upwards of twenty feet in length, 

 and these were of such a size as to indicate a height of forty or fifty 

 feet when entire. They appear to have attained maturity. 



" In the conversion of the bark into lignite, and in the smooth con- 

 dition of the trunks, this fossil forest presents a remarkable dissimi- 

 larity from that of the Isle of Portland, in which, so far as I have 

 observed, the carbonized bark rarely, if ever, occurs, and the sur- 

 face of the stems is similar to that exhibited by the trunks of old 

 decorticated trees that have been much weathered by alternate ex- 

 posure to air and moisture. At Brook Point, on the other hand, 

 the trees appear to have been engulfed when fresh and vigorous, 

 and when their bark and vessels were full of sap. The annular lines 

 of growth are often very distinct, and I have traced from thirty to 

 forty on some of the stems, but these circles are unequal, and indi- 

 cate therefore a variation from year to year in the climate of the 

 country in which they grew. The wood exhibits, under the micro- 

 scope, coniferous structure of the type seen in the Araucaria (Nor- 

 folk Island Pine), the rows of glands or ducts being placed alter- 

 nately, and the appearance being similar to that of the fossil wood 

 of Willingdon in Sussex*. I observed no trace of the foliage of 

 these trees, nor of their fruit, with the exception of a small cone, 

 scarcely so large as that of the larch f. 



" In the strata that overlie the fossil forest, thin interrupted seams 

 and irregular masses of lignite are very abundant, and their substance 

 is more or less impregnated with and perm.eated by iron pyrites. 

 Fossils similar to these occur also in the clays of Tilgate Forest and 

 at Hastings. 



" The various conditions in which the remains of vegetables are 

 preserved in the Wealden strata suggest many interesting inquiries. 

 Why, for instance, is the bark so much more frequently carbonized 

 than the woody fibre ? Why do the trunks of Coniferae occur in 

 the state of coal in the old carboniferous strata and not in the de- 

 posits before us ? What conditions occasioned the difference ob- 

 servable in the state of the fossil trees at Brook Point and at Port- 

 land ? Why has the Endogenites erosa of the Wealden (a monoco- 

 tyledonous tree) always a thick coat of lignite, while the Clathraria 

 (a plant allied to the Yucca) is never carbonized? And lastly, is 

 the interpretation of these phoenomena to be sought for in the ori- 

 ginal organization of the plant, or in the state of the trees at the 

 period of their submergence, or in the conditions of deposit, whether 

 mineral or with reference to the degree by which they were affected 

 by air and moisture ? J " 



* Quart. Geol. Journ. vol. ii. p. 51 ; Medals of Creation, p.l66, pi. 5. f. 3. 



f Two cones (now in the possession of Mr. Dixon) have been obtained from 

 the Isle of Wight, probably from the Wealden strata ; but their locality being un- 

 certain, no satisfactory evidence is afforded of their relation to the fossil trees 

 under consideration. 



X The author suggests that a white calcareous incrustation observed on many 

 fossil bones obtained from this spot may probably be derived from the fresh-water 

 springs that percolate through the strata of the cliff, which ai'C composed of clay, 



