30 



emulating the vegetable forms, becoming blended with the 

 real vegetable ; and from the actual investment of the whole 

 plant with carbonate of iron ; but the most common source 

 of deception and obscurity, in the Doctor's opinion, " will be 

 found in the whimsical and fibrous disposition occasionally 

 assumed by chlorite, its colour often imitating the natural 

 hue of a plant as perfectly as its fibrous and ramified 

 appearance does the disposition and form of one." All the 

 plants that have been discovered in this state of envelope- 

 ment in quartz appear to belong to certain species of the 

 cryptogamia class, chiefly byssi, confervae, jungermanniae, 

 and the mosses. The stones found at Dunglas, Dr. Mac- 

 culloch observes, " contain remains of organized substances 

 of an epocha at least equally ancient with that in which the 

 vegetable remains found in thefloetz strata existed. As the 

 species ascertained by Daubenton have, in all probability, 

 been preserved in recent formations of chalcedony," so the 

 Doctor thinks that " those which he describes have been 

 preserved in the chalcedonies of former days*." 



The moss agates of the Yorkshire coast appear to be of 

 the ancient, whilst other specimens which I possess from 

 Iceland prove the correctness of Dr. Macculloch's opinion, 

 that some of these fossils are of recent formation. 



The remarks of Dr. Macculloch on the mode in which 

 these curious investments were accomplished, deserve 

 particular attention. " The remains are, in fact, (if I may 

 use such an expression) embalmed alive. To produce this 

 effect, we can only conceive a solution of silex in water, 

 so dense as to support the weight of the substance in- 

 volved, a solution capable of solidifying in a short space 

 of time, or capable at least of suddenly gelatinizing pre- 

 viously to the ultimate change by which it became solidified 

 into stonef." 



* Geological Transactions, vol. ii. p. 511, 518. 

 t Ibid. vol. ii. p. 522. 



