OF THE STRUCTURE OF WOOD AND HERBS. 97 



precision many portions of the ancient vegetable history of our globe, legibly 

 imprinted in its fossil woods and plants. So perfectly has their structure been 

 preserved for ages, that the skilful observer easily detects the various species, 

 and assigns them their appropriate place in the vegetable kingdom. The sub- 

 stance of these woods, as Mantell remarks, is completely permeated by mineral 

 matter. It may be lime, flint, iron, or iron united with sulphur ; and yet both 

 the external character and internal structure be preserved. Such are the fossil 

 trees of the Isle of Portland, where a whole forest of Pines seems to have been 

 transformed into stone, on the very spot where they grew and flourished : the 

 roots of the trunks changed into flint, piercing deep into the soil whence they 

 sprung. Fragments of these trees so closely resemble decayed wood, that a 

 person who bestows upon them only a casual glance is completely deceived ; 

 but, by close examination of their texture and substance, he finds that they pos- 

 sess the weight and hardness of stone. In wood petrified by flint the most 

 delicate tissues of the original remain uninjured, and are displayed under the mi- 

 croscope in the most beautiful and distinct manner. Wood petrified by lime 

 also retains its structure, and in many limestones leaves and seed-vessels are 

 faithfully preserved. 



In the Egyptian and Lybian deserts, a numerous assemblage of trees has been 

 discovered, petrified by flint. Fragments are found everywhere scattered over 

 this arid region, but the most interesting locality is a table-land, about seven 

 miles south-east of Cairo, where the trees are found in such numbers that it is 

 termed the Petrified forest. Here huge trunks of flint are seen crossing each 

 other in every direction, as if swept down by the irresistible force of a hurri- 

 cane. 



Two of the largest, the dimensions of which were taken by Col. Head, who 

 visited this spot, measured respectively forty-eight and sixty feet in length, and 

 two and a half and three feet in diameter at the base. In the rich specimens 

 collected by him from this locality, the most delicate cells and veins of the 

 interior stricture of the wood are filled with chalcedony and jasper, and some 

 of the vessels, injected with flint of a bright vermilion and blue color, traverse 

 the cellular tissue, which gleams with a golden hue. 



Not only on the surface of the ground are petrified trees discovered, but they 

 have been brought to the light from a depth of more than one hundred feet ; 

 where, notwithstanding they had been buried for ages, their structure was so 

 perfect, that the species to which they belonged was at once identified. To 

 effect this result a transverse or longitudinal section of the fossil specimen to be 

 examined is obtained, which, after being cemented to a slip of glass, with Cana- 

 dian balsam, is ground down with emery, until it becomes sufficiently thin for 

 its structure to be perceived under the microscope. When the section is thus 

 properly prepared, and magnified from one to four hundred times, the pecu- 

 liarities in the structure of the wood are revealed with great distinctness. 



Four specimens of fossil woods are delineated in figures 147, 148, 149, 

 and 150; and by comparing them with the figures 137, 138, and 139, 



