32 



so particular and exact as to yield positive evidence of their 

 original nature ; and, as has been already shown, the in- 

 stances are by no means infrequent in which the traces, 

 and even the remains of cactuses and other succulent plants, 

 had given rise to the belief of the existence of fossil trees 

 in these strata. This opinion may therefore have obtained 

 seeming confirmation from the ligneous hardness which 

 large plants of this kind might have acquired, and which, 

 perhaps, might be traced in their mineralized remains. 



The earliest stratification in which fossil wood exists 

 is not perhaps at present determined ; but it seems that the 

 earliest appearance in this island of fossil wood, which by 

 its uniformity of character appears to belong to a particular 

 bed, is the spathose bituminous wood of the blue lyas, as 

 found at Lyme in Dorsetshire, and in the neighbourhood of 

 Bath (p. 22). In the next formation, and particularly in 

 that of the green sand, siliceous fossil wood occurs fre- 

 quently. Very delicate specimens are found in the sand- 

 stone, the whet-stone of the Blackdown hills of Devonshire. 

 The specimens of fossil wood found in the Portland stone 

 are frequently of very considerable size, and bear all the 

 characteristic marks of wood : these are also siliceous, and 

 are often beautifully sprinkled on their interior surfaces 

 with quartz crystals. Siliceous fossil wood is also found in 

 other situations, as in the sands of Wooburn in Bedford- 

 shire : it also occurs at Folkstone in Kent, in that part of 

 the green sand where it approximates to the superincumbent 

 marl, in which it is also found. Traces of wood are hardly 

 ever discovered in the chalk itself, and so rarely in the 

 accompanying flint nodules, that the knowledge of but one 

 specimen, an instance of this occurrence, is known to the 

 writer of these pages. But in the blue clay, incumbent 

 upon this immense accumulation of chalk, fossil wood, 

 pierced with teredines, and impregnated with calcareous 

 spar, is exceedingly abundant : and in almost every sunken 



