Page images


described, its formation may, perhaps, be accounted for on the same principles as the formation of all true veins ; but where there is a succession of floors, if junctions of lodes could be satisfactorily shown at every point where they occur, it would give us little assistance in forming a theory of their formation. We have been accustomed to consider the contents of the tin lodes as of posterior formation to the rocks which contain them; but here is a succession of beds, all of them connected with tin lodes (for they are always found on one or both sides of tin lodes, to which, when they are not quite close, they are united by a small branch), and yet alternating with the rocks of the country, which are supposed to be older than the tin lodes. It is not surprising that the practical miner troubles himself little respecting the theory of the formation of the metalliferous bodies which he may discover ; but it is indeed extraordinary (as Mr. Hawkins has observed in his paper on tin floors), that in a district where so large a quantity of tin has been found in floors, there is not more diligence and perseverance evinced in searching for those deposits.

* Formation of Sandstone.--In Pendeen Cove, which forms the northern boundary of this parish, the sand consists principally of comminuted shells, mixed with particles of slate, and of the constituent parts of granite. The cliff which bounds the cove is rather precipitous, and in one part consists of large fragments of granite imbedded in clay and earth. The interstices of this cliff are filled with sand (probably blown there from the beach by high winds); which is exposed to the percolation of water holding in solution the oxide of iron, whose cementing property is well known. The sand is thus gradually becoming stone, and in some parts of the cliff it has already acquired considerable hardness."*

“ In the Cliff near Little Bounds Mine, the same operation is going forward, but the sand is more granitic than at Penden Cove."

XVI. On the Knowledge and Commerce of Tin Nations. By the Rev. Samuel Greatheed. (Communicated by John Dennis, Esq. MGSC.)

This paper is entirely archæological.

XVII. On the Geology of St. Michael's Mount. By John Forbes, MD. &c.

We can only quote some concluding passages of this commu nication :

“Much has been said respecting the relative age of different granitic rocks in different countries, and among others, respecting that of St. Michael's Mount, which has by some late writers

among ancient

* " As this sand appears in some cases to extend further than the face or the intera stices of the cliff, some have supposed a body of it to have covered the ancient surface, either by the means of high winds, or other causes, before the superincumbent mass of clay and granite fragments was placed there."


[ocr errors]

been stated to be of that class of rocks denominated transition by the Wernerian School. Of the existence any where of a class of rocks entitled to this name, I have great doubt; of the impropriety of considering the granite of St. Michael's Mount as of a different age and formation from that'of the rest of Cornwall, I have no doubt whatever; and the appearances adduced by some writers as indicating posterior formation, are either imaginary or fallacious, or are common in other parts of the country, which are considered by these very geologists as primitive. Although the existence of strata of slate dipping under granite, and of beds or strata of granite resting on, and alternating with, slate, would not be a decisive proof, in my estimation, that one of those rocks was formed before the other; it is but justice to state that the accounts which describe such alterna

tions as occurring at St. Michael's Mount, are totally erroneous; ; and I have no hesitation in saying, that there is no instance to

be found in the whole of the Land's End district, where any thing like a bed of granite is found resting on slate. I

may here notice a circumstance that may tend to throw some light on the veined structure of St. Michael's Mount, that it shares this character with several other spots on these shores, where the main body of the granite is in contact with the slaty rocks. This is more especially remarkable at Polmear, in Zennor; and in the neighbourhood of the Logan Rock. Indeed, I consider these quartz veins, and the true shorl rock veins mentioned in a former paper, as mere varieties of the same substance.”

XVIII. On some Instances of the alternate Disposition of the primitive Strata which have been observed in Cornwall. By John Hawkins, Esq. FRS. &c.

This article relates to an apparent alternation of granite and clayslate observed in several mines near the line of junction of those rocks, which has already been described in Mr. Thomas's Survey of the Mining District of the County; as well, we believe, as in other publications.

XIX. On the Tin Ore of Botallack and Levant. By Henry S. Boase, MD. Sec. GSC.

The processes of dressing and smelting the mixed tin and copper ores of Botallack and Levant, as described by Dr. Boase, present nothing remarkable, nor are his explanation and suggestions for the improvement of them possessed of greater interest, though calculated to be highly useful to those persons, practically engaged in such concerns, who are unacquainted with chemistry. The paper contains, however, the following interesting account of a specimen of tin pyrites, from a new locality:

“Here I would digress for a moment to notice a very interesting discovery, accidentally made, of tin pyrites, which has been no where found, I believe, except at Huel Rock, in St. Agnes ; Slenna-gwyn, in St. Stephens; and Huel Scorier, in Gwennap. I had desired a workman employed at the stamping-mill and burning-house at Botherris, to send me three specimens of tin ore containing copper, one of which I found to be an aggregation of yellow copper ore and tinstone, another of grey copper ore and tinstone ; but the third, to my great surprise, had a compact uniform structure, perfectly homogeneous in appearance, resembling tin pyrites in all its external characters; and on comparing it with the specimens in our cabinet, it agreed in every respect, except that its colour was a little lighter, with rather more of metallic lustre. To determine its nature with greater certainty, this substance was submitted to the following experiments : When exposed to a red heat in a covered crucible,

. it lost weight, and sulphur was sublimed: calcined with free admission of air, sulphurous acid gas was evolved; it increased in bulk; changed to a dark-brown colour, and lost 15 per cent. in weight. In nitromuriatic acid it readily dissolved without the application of heat, and during solution, nitric oxide gas was disengaged. Intending subsequently a more accurate analysis, a rough one was performed after the method proposed by Klaproth. The result was, in 100 parts : Copper

31 Tin..

28 Iron,

6 Sulphur..

25 Silica, with a little alumina

7 Loss.


[ocr errors]


The loss was probably occasioned by some of the sulphur (during the solution of the mineral in the acid) escaping in the form of sulphuric acid gas. This analysis proves beyond' doubt that the mineral was tin pyrites."

Dr. Boase was unable to procure even another specimen of this mineral from Botallack ; but it appears that the one just described came from that part of the mine which is called Huel Hazard.

XX. On the Temperature of the Cornish Mines. By M. P. Moyle, Esq. MGSC.

XXÍ. On the Serpentine District of Cornwall. By the Rev., John Rogers, MGSC. This paper, like the former one by the same author, consists

, of local details unsusceptible of abbreviation : they are chiefly confined to some circumstances of the interesting district in question, which, Mr. Rogers states, have escaped the notice of Mr. Majendie and of Prof. Sedgwick, in their respective surveys of it.

A series of tables of the quantities of tin and copper raised in Cornwall in different years, those of the former metal com

mencing in the year 1750, and ending in 1821, and those of the latter beginning in 1771, and terminating in 1822, with several others of the quantities of copper produced by the various mining districts of the kingdom from 1818 to 1822; a list of donations to the Society; and another of the minerals wanted to complete its cabinet, close the volume.


Narrative of a Journey to the Shores of the Polar Sea, in the

Years 1819, 1820, 1821, and 1822. By John Franklin, Capt. RN. FRS. and Commander of the Expedition. With an Appendix on various Subjects relating to Science and Natural History. Illustrated by numerous Plates and Maps. Published by Authority of the Right Honourable the Eart Bathurst.

(Concluded from vol. v. p. 387.) We intended, in the present article, to have given a minute analysis of the Appendix to Capt. Franklin's Narrative; omitting any notice of that narrative itself, on account of the numerous channels of general information through which the public either are or will be made acquainted with its contents. Such, however, is the variety and importance of the scientific information comprised in the Appendix, occupying two hundred and seventy closely printed quarto pages, that it would be impossible, within the space allotted to this department of the Annals, to give even the semblance of a detailed account of it. The utmost we can do, therefore, is to present our readers with an enlarged table of the contents of this Appen

and as we inserted two papers from it on the Aurora Borealis, in the commencement of the article, we will subjoin a few observations selected from several others; in order that the reader may possess some satisfactory knowledge, of at least one of the subjects principally treated of, by the indefatigable traveller and his no less indefatigable coadjutors. At some future opportunity, perhaps, we may transfer to our pages some further portions of their labours :

The following are the contents of the Appendix in question : No. 1.-Geognostical Observations; by John Richardson, MD. and Surgeon to the Expedition. 41 pages.

No. 2.- Aurora Borealis. 9 pages; including Capt. Franklin's General Remarks, and Lieut. Hood's Observations, given in the Annals for May ;-with An Account of the Aurora Borealis seen at Cumberland House between Oct. 23, 1819, and June 13, 1820, by the latter officer;—and Observations on the Magnetic Needle at Cumberland House, from the beginning of Feb. to the end of May, 1820, by the same. No. 3.

Observations on the Aurora at Fort Entreprise ; and Notices of the Appearances of the Aurora, at the same place; both by Capt. Franklin :- Table of Observations on the Devia


[ocr errors]


tions of the Magnetic Needle, made at Fort Entreprise, from Jan. 12 to April 9, 1821:-On the Aurora Borealis at Fort Entreprise; Appearances of the Aurora at the same place; and a Table of the Diurnal Variation of the Needle there; all by Lieut. Hood :-Remarks on the Aurora Borealis, by Dr. Richard

In all 79 pages. No. 4.-Remarks and Tables connected with Astronomical Observations ; 17 pages : including, Three Tables of the Diurnal Variation ;-General Remarks on the Variation of Kater's Compasses, observed during the Journey in North America, and along the Arctic Sea ;-Results of the Observations for Latitude, Longitude, and Variation ;-Table of Observations on the Dip of the Magnetic Needle, between York Factory and Point Turnagain ;-Table of Observations on the Magnetic Force ;--Tables of Temperatures ;-General Tabular View of the Winds and Weather for One Year, 1820, 1821 ;-Various Observations on the Passage to Hudson's Bay.

No.5.--Zoological Appendix; by J. Sabine, Esq. 56 pages:
No. 6.--Notices of the Fishes; by Dr. Richardson. 24 pages.

No.7.-Botanical Appendix ; by Dr. Richardson. 40 pages; describing 663 species of plants :- Addenda, by Robert Brown, FRS.

We proceed to select some observations on the Aurora Borealis : the following are by Capt. Franklin, made at Fort Entreprise, in lat. 64° 28' 24" N.; long. 113° 6' 0"W.

“ The arches of the Aurora most commonly traverse the sky, nearly at right angles to the magnetic meridian, but the deviations from this direction were not rare; and I am inclined to consider, that these different positions of the Aurora have cousiderable influence upon the direction of the needle. When an arch was nearly at right angles to the magnetic meridian, the motion of the needle was towards the west; this westward motion was still ater when one extremity of an arch bore 301°, (or about 59° to the west of the magnetic north), that is, when the extremity of the arch approached from the west towards the magnetic north. A westerly motion also took place when the extremity of an arch was in the true north, or about 36° to the west of the magnetic north, but not in so great a degree as when its bearing was about 301o. A contrary effect was produced when the same end of an arch originated to the southward of the magnetic west, viz. when it, bore from about 245° to 234°; and, of course, when its opposite extremity approached nearer to the magnetic north. In these cases, I say, the motion of the needle was towards the east.”

In one instance only, a complete arch was formed in the

« PreviousContinue »