Page:Proceedings of the Royal Society of London Vol 1.djvu/180

Rh schistus found at Reykum, one of the great spouting hot springs in Iceland. The singularity of this substance is, that a great part of it consists of leaves, (evidently those of the alder,) interposed between the diﬁ'erent lamellae. These leaves appeared to be in the state of charcoal; but on more close examination, no doubt remained of their still retaining a certain portion of some of the other principles of the original vegetable, such as extract and resin. This, in fact, is the result of an extensive chemical process, from which we learn that the schistus, taken collectively, yields, besides silicia, alumina, and oxide of iron, a certain proportion of water and of vegetable matter, and that it evidently belongs to the family of argillaceous schistus.

The above process may be considered as preliminary to that on the Bovey coal, in which the vegetable characters are more obliterated than in the leaves of the schistus. This coal, we are told, bears a great resemblance to a fossil found in Iceland, called Surturbrand; the strata of both being composed of trunks of trees, which have completely lost their cylindrical form, and are ﬂattened, as if they had been subjected to an immense degree of pressure. On inquiring into this last-mentioned circumstance, our author produces his rea- sons for believing that it is not the effect of the mere pressure of a super-incumbent stratum, but also of a certain change in the solidity of the vegetable bodies, and a powerful mechanical action, produced by the contraction of the argillaceous strata in consequence of desic- cation.

Here follows the analysis of the Bovey coal. The results point out a great resemblance between this substance and that which forms the leaves contained in the Iceland schistus. The only exception is, that the leaves contain some vegetable extract, none of which could be discovered in the coal. Both consist of woody ﬁbre in a state of semicarbonization, impregnated with bitumen and a small portion of resin, perfectly similar to that which is contained in many recent vegetable characters, and is but partially and imperfectly converted into coal; so, in like manner, some of the other vegetable princi- ples have only suﬁ'ered a partial change. Next to this woody ﬁbre, resin is thought to be the substance which, in vegetablm passing to the fossil state, most powerftu resists any alteration, and which, when this change is at length eﬂ’ected, is more immediately the sub- stance from which bitumen is produced.

This opinion, that the vegetable extract and resin are the parts of the original vegetables, which retain their nature after other portions of the same have been modiﬁed into bitumen, is corroborated by the analysis which here follows, of a singular substance which is found with the Bovey coal. Dr. Milles, who ﬁrst mentioned this substance, considered it as a loam saturated with petroleum; but our author, on mere inspection, decided that it is not a loam, but a peculiar bituminous substance. After a description of its external appearances, and some of its relative properties, we come to the analysis; from which we collect, that this is a peculiar and hitherto unknown substance, which is partly in the state of vegetable resin, and partly in