Pyrites in Septaria
- Div. 2. Amorphous.
The opening of the tunnel at Highgate has been a source of much information to the metropolis, with regard to extraneous fossils more particularly, and will extend information much more than could have been expected.
In many respects the hill resembles the cliffs of Shepey in soil and contents. The upper soil is loamy for a few yards, and below is a dark clay. There are septaria in the inner part of the more ochraceous clayey loam, which partake of the ochraceous appearance, and others which are more abundant, and lay more or less level with each other in rows in the dark clay; the most compressed and regular ones uppermost. They vary in size, from that of a small round tennis-ball to two or three feet in length and breadth, often nearly one foot in thickness. Those in the dark clay are more indurated than those in the stratum above; the divisions or septa darker, in general varying from yellowish to bright reddish brown*. The Tali vary, but are mostly of a darkish gray or brown colour, lighter when dry. The open parts of the divisions frequently contain water, nearly resembling rain water; they are rather remarkable for containing indiscriminately in their structure many shells of different species, and some, I believe, new to us at present; some that belong to distant climates, and some very rarely found at Shepey, Hordwell Cliffs, &c. These are also more or less dispersed in the dark clay. Remains of various fishes, crabs, teeth, &c, are also mingled occasionally in the ludi, and, like those from Shepey, they have the stellated Sulphate of Barytes (see tabs. 172 and 173,) upon some of them, but very rarely.
Although these septaria abound more or less in all clay pits, wells, &c. in and about London, as well as other clay soils, they have, from the novelty of a tunnel, been ardently gathered by all sorts of people, and claimed extraordinary attention.
The rarest of the Septaria, according to Sir John Hill, is the Pyriteria, by which appellation he calls those Septaria or his Sceomia that are divided by Pyrites or Sulphuret of Iron. I have therefore figured a fragment of one, found about the middle of the tunnel, about 90 feet from the surface, as an example in this work. It is not only divided by the neat brilliant septa of Sulphuret of Iron, but that is again divided by a portion of Carbonate of Lime, and it also happens to have a transverse section of a shell, and a specimen of Murex Trapezium? upon it; (see Linn. Syst. ed, 13. p. 3552 and 3553. Rumph. 29. fig. C. is perhaps the best figure,) a shell not uncommonly found in the East Indian ocean and at Amboyna: but there seems much confusion in the description and references, and the foreign shell has a plicated column, which the Highgate one has not:—but more of this in its proper place, if I should treat of the other Highgate shells.
The many varieties of Septaria mentioned by Hill are superfluous, being about 30: the above descriptions, with our figures tab. 61, and the Septarium of Quartz, tab. 207, will nearly include all. The former often contain remains of wood in various slates of decomposition, perforated by the Teredo navalis, Linn. partly like the upper figure, tab. 200. This terrible animal is said to have been imported from India!
The common Septaria are used as stucco for ornaments on houses, out-door walls, &c, and is called Parker’s cement, (at which 1 hinted in the description of tab. 14.) when prepared by bating; and, if well prepared, is very durable.
The finding a species of resinous Bitumen at Highgate is a curious circumstance; it has been found attached to these Septaria. I shall not fail to insert a further account of this substance, as another feature in the British catalogue.
- * Argilliferous Marlite, Kirw. 1. 99.