preserved in Chalcedony, 525 



- IS. Exhibits a remarkable instance of a deposit of reddish oxide 

 of iron, modified by a white central fibre, with whose nature I 

 am unacquainted. 



14. I suspect that this consists of grains of chlorite, become 

 brown from some of the changes to which I alluded in the paper, 

 and surrounded with an additional metallic covering. 



15. The ramified structure of this is too decided to admit of its 

 being any thing but a vegetable substance ; possibly it is the root of 

 some moss. 



IG. In the chalcedonies, which go by the name of Mochas, 

 brown arborizations are known to be very common, and often to 

 assume appearances which render these stones much sought after 

 for ornaments. I have here figured one which bears so strong a 

 resemblance to the imbricated Jangermannise, that it is difficult at 

 first sight to distinguish them. The detached scales render the de- 

 ception still stronger, their appearance being that of leaves which 

 have been broken o^. But it will I believe be found that all these 

 are metallic. How much soever, the bases or middle parts of the 

 pretended plants may put on an appearance difficult to discriminate, 

 it will almost always be found that the extremities of the branches 

 are undefined and shapeless, while in the Jungermannias the regular 

 imbrication of the scales is continued to the minutest extremity. 

 The eye of a botanist will also with care discover an irregularity in 

 the superposition of the scales, which never occurs in the plants 

 themselves, and a decision in the setting on of the branches in the 

 real plants, which is ill imitated by the clumsy v;ay in which the 

 ramifications are disposed in the metallic arborization. I do not 

 however mean to deny that these stones may not contain organized 

 bodies, as I have below given a figure of such an one. 



17. Fibres, very common in chalcedonies, and bearing a consi- 

 derable resemblance to Byssus nigra, — conferva ebenea of Dillwyn. 



