16 REMARKS ON THE DISTINCTIVE CHAItACTERS 



Of the fossil plants which I have examined with reference to their in- 

 ternal organization, none belong to the first two classes ; nor is it likely that 

 the delicate and fragile texture of Algae and Mosses could be preserved in a 

 petrified state. Those which I shall describe in the present work belong to 

 the third and fourth classes. 



At the date of the publication of my Observations on Fossil Vege- 

 tables, the attention of geologists had been exclusively confined to the ex- 

 ternal forms of fossil plants ; and these forms, illustrated by reference to 

 living species, and to vegetable anatomy, have afforded characters by which 

 numerous species and genera maybe distinguished with accuracy. But the 

 supposed destruction of the internal structure of most fossil plants, and the 

 difficulty of applying the microscope to those which evidently retain it, 

 had prevented our becoming acquainted with the organization of these plants. 

 Many fossil vegetables are converted into a mass of carbonaceous matter ; 

 others are filled up with sand and other substances, the external or cortical 

 part alor.e remaining ; but it has been found that not a few retain their 

 original structure, the interstices being filled up by calcareous or siliceous 

 crystallizations. Plants which have been preserved in this manner, fre- 

 quently disclose their organization as plainly as recent vegetables of like 

 families ; but it is more difficult to prepare them for examination. 



It will be sufficient here to describe this method very briefly. A thin 

 slice is first cut from the fossil wood, in a direction parallel or perpendicu- 

 lar to the fibres. It is ground flat and polished on one side, which is at- 

 tached, by means of Canada balsam, to a piece of plate-glass, after which it 

 is ground down to the necessary degree of thinness, and polished. By this 

 means, the internal structure may frequently be as distinctly seen as in the 

 slice of a recent vegetable. 



As might be supposed, the remains of the internal organization thus 

 displayed, are frequently distorted and disrupted in various ways, crushed 

 into confused masses, or widely distended and separated. In examining 

 them, therefore, caution is required, lest the regular be confounded with 

 that which has been modified by various causes. The crystallization of the 

 infiltrated substance has operated powerfully, among other causes, in pro- 



