preserved in Chalcedony., 523 



solidifying in a short space of time, or capable at least of suddenly- 

 gelatinizing previously to the ultimate change by which it became 

 solidified into stone. I need not point out the extreme importance 

 of this supposition, I had almost said of this fact, to any general 

 theory of the earth. It is for chemistry yet to investigate experi- 

 mentally the mode of imitating this unknown process. Those who 

 know the present state of this science will not hesitate to admit its 

 imperfections, and those who have attended to its rapid progress 

 will not despair. 



Description of Figures, PI. S6. 37. 



No. 1. I think the peculiar membranes and defined structure 

 seen in this figure can only arise from a plant, although I am not 

 acquainted with any analogous living vegetable. I had not enough 

 to subject it to chemical trial. 



2. This figure exhibits one of the most common forms in which 

 chlorite is disposed in chalcedonies, a form not very likely to mis- 

 lead an observer. 



3. I have figured this for the purpose of shewing the remarkable 

 imitation of a conferva, which may be produced by chlorite ; that 

 part of the drawing which is most highly magnified, exhibiting a 

 chain which consists of distinct scales of this substance. 



4. Is drawn from a specimen which appears to contain fragments 

 of two plants ; a conferva, and the leaves of some other plant, 

 perhaps a moss. 



5. That this drawing is made from a plant, I have ascertained 

 by chemical trial, and the green spots which seem disseminated 

 along the fibre are probably the fructification. 



6. This specirtien exhibits an internal structure, not very unlike 



3u 2 



