13. 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.
16. 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 Jungermanniæ, that it is difficult at first sight to distinguish them. The detached scales render the deception still stronger, their appearance being that of leaves which have been broken off. 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 Jungermanniæ 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 way 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 considerable resemblance to Byssus nigra,—conferva ebenea of Dillwyn.