Silicious Iron-Stone

Many places afford Iron-stones, Geods, &c. See Descriptions and Plates 106 and 107^*. The present specimen is from under the Thames at Rot her hi the, where the Tunnel is perforated, in a mixture of Sand, Sandy Lime, &c. It is remarkable for its branching, and in some specimens so much so as to represent the more entangled roots of trees. It is internally of a raw brown umber colour,, nearly compact appearance, and may be scratched with a pin, giving a whitish streak: externally more or less rugged, with Lime and Sand attached to it. I have only one instance of its being found elsewhere, and that is a larger specimen in the possession of Mr. Smith, who is so well known to be conversant with most of the Strata of this Island, who found it in Wiltshire. The Iron in this specimen is in a low state of oxidizement, and is intimately combined with Silex and other earthy matter, as with a little heat it becomes magnetic. Some of my specimens are the more extraordinary for having little Geods about the size of hazel-nuts, with a coat or outward crust nearly the colour of the shell of those nuts, and an ochre resembling Roman ochre, more or less loose within them. Thus we have an use for the term or division Imitative, from the resemblance of these to the branches of trees and nuts. In many instances Nature’s works are so extraordinary in these productions as to elude the nicest discernment, and teach us that much experience is necessary to prevent error.