SEPTARIA OF IRON-STONE. Over some lime works at Walsall in Staffordshire, I observed some years ago a stratum of iron earth about six inches thick, full of very large cavities; these cavities were evidently produced when the material passed from a semifluid state into a solid one; as the frit of the potters, or a mixture of clay and water is liable to crack in drying; which is owing to the further contraction of the internal part, after the crust is become hard. These hollows are liable to receive extraneous matter, as I believe gypsum, and sometimes spar, and even lead; a curious specimen of the last was presented to me by Mr. Darby of Colebrook Dale, which contains in its cavity some ounces of lead-ore. But there are other septaria of iron-stone which seem to have had a very different origin, their cavities having been formed in cooling or congealing from an ignited state, as is ingeniously deduced by Dr. Hutton from their internal structure. Edinb. Transact. Vol. I. p. 246. The volcanic origin of these curious septaria appears to me to be further evinced from their form and the places where they are found. They consist of oblate spheroids and are found in many parts of the earth totally detached from the beds in which they lie, as at East Lothian in Scotland. Two of these, which now lie before me, were found with many others immersed in argillaceous shale or shiver, surrounded by broken limestone mountains at Bradbourn near Ashbourn in Derbyshire, and were presented to me by Mr. Buxton, a gentleman of that town. One of these is about fifteen inches in its equatorial diameter, and about six inches in its polar one, and contains beautiful star-like septaria incrusted and in part filled with calcareous spar. The other is about eight inches in its equatorial diameter, and about four inches in its polar diameter, and is quite solid, but shews on its internal surface marks of different colours, as if a beginning separation had taken place. Now as these septaria contain fifty per cent, of iron, according to Dr. Hutton, they would soften or melt into a semifluid globule by subterraneous fire by less heat than the limestone in their vicinity; and if they were ejected through a hole or fissure would gain a circular motion along with their progressive one by their greater friction or adhesion to one side of the hole. This whirling motion would produce the oblate spheroidical form which they possess, and which as far as I know can not in any other way be accounted for. They would then harden in the air as they rose into the colder parts of the atmosphere; and as they descended into so soft a material as shale or shiver, their forms would not be injured in their fall; and their presence in materials so different from themselves becomes accounted for.