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been noticed, that these disintegrated tracts exhibit frequent patches of various dimensions retaining their original compactness. It would be a point of some geological interest to ascertain, as accurately as circumstances permit, the extent to which this disintegration actually obtains, and to enquire whether the tracts in question exhibit any phenomena which might guide our speculations as to its probable cause. That that cause is not to be sought in the mere superficial action of weather and moisture, we may, I think, argue from the great depth to which (as at Carglaise) the disintegration is found to extend. I have heard it suggested, that this state of granitic rocks is to be regarded rather as the mode of their original formation than as the result of causes acting subsequently. This hypothesis, however, seems hardly reconcileable to the appearances presented by Carglaise. Some may, perhaps, incline to view the phenomenon as analogous to the disintegration which is known to obtain largely in crystalline rocks forming acknowledged dykes,* and to these it may appear to countenance the theory which attributes to granite an igneous origin. At all events, this species of decomposition seems for the most part peculiar to rocks of a crystalline structure. In some cases, if my observation be correct, the granite is traversed by porphyritic dykes, or elvans, similar to those occurring in the slate. I noticed one (in company with Mr. Buckland) in 1812 on the summit of Kitt Hill, near Callington. In some cases too the saalbande, or wall of metalliferous veins traversing the granite, appears to be of this class. At Bean Mine, about one mile east of Roche, the surrounding country is granite of the usual aspect; while the walls of the tin lode which are of considerable thickness have all the character of an elvan dyke, the paste of which is chiefly quartzose with a mixture of mica, talcite, felspar much disintegrated, and crystallized shorl, the tin occurring in veins with shorl towards the centre of this elvan (the veins occasionally send out small lateral branches at various angles), the elvan itself is said to dip three feet in the fathom, and in its general character much resembles some of those found to the east of St. Agnes. The same inclusion (if I may so term it) of a metallic vein by a rock differing from the surrounding granite I recollect to have noticed also at Newbridge, and in the Gwennap cluster. It would be desirable to

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to a much greater distance from the top of the hill, would have been taken to be granite, as the surface has every appearance of a growan soil intermixed with granite stones and rocks plentifully scattered about. The same has been observed on the sides of Carn Marth and other granite hills bordering on the Killas country.” We were assured that at Newbridge they had sunk above the granite country in a mass of granitic rubble with occasional blocks of killas intermixed to the depth of nearly 30 yards, and above the killas country in a rubble of that rock with a small admixture of killas to about half that depth.

* See Mr. Henslow's Account of Anglesea. (Cambridge Philosophical Transactions, Part II.)

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ascertain how far this is the case in veins which traverse granite.

At Kit Hill above-mentioned, at Carglaise, and at some other places, we were assured by miners apparently of competent information, that the granite did in some places overlie the killas. In these instances, it is possible that granitic dykes may have been mistaken for the central mass, or that our informants might have been misled by some of those deceptive appearances which are familiar to most geologists. Mr. Taylor, in his excellent Survey of the Mining District, mentions an analogous fact, and his observation is too important to be omitted. “In Dolcoath and five other mines situate near the junction, the strata of granite and killas appear alternately overlying each other, the divisions between them being at various inclinations ;* but sufficient information cannot be obtained to state with accuracy the particulars.”+

On the subject of granitic veins, my memoranda afford nothing which can add to the copious and masterly observations of Mr. Sedgwick. I may mention, however, that the country near the junctions of Carn-brae, of Kit Hill, of the upper part of the river Okement, and of some other spots of the same character, will afford the collector hand specimens well calculated to illustrate on a small scale many of the phenomena which present themselves so fully and magnificently at the cliffs of Trewavas and Polmear.

It may here be noticed, that the mineral substances confined to the granite (or rather not yet discovered in the superincumbent rocks also), are few in number. Apatite, pinite, andalusite, and, I believe, uranite, at present complete the list.

Shorl Rock.--This binary compound, too generally known to need any description here, is usually found on the confines of the granite in such large masses as to render us doubtful what name to assign to them. Indeed our geological guides have not as yet furnished us with a very definite or accurate terminology for the purpose. What one observer would describe as a large dyke or patch, another would, perhaps, elevate to the dignity of a formation. Roche has been constantly noticed as presenting a magnificent display of this rock; and Mr. Sedgwick mentions it as occurring in veins traversing the granite between Lemorna Cove and the Land's End (p. 19). I have observed it on the large scale forming the whole of the tor named Carn Mewan,

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* Therefore, if there is any parallelism in the stratification of the killas, the granite must be considered not as an alternation but a vein. At Dolcoath, the floor of granite is said to be nearly horizontal ; most of the killas in the neighbourhood is, if I do not err, considerably inclined. (See Thomas's Report, p. 34.)

* Mr. Sedgwick appears to have determined this point as far as our present means of examination permit. (P. 34.)

# We obtained some highly illustrative at Costellow's Mine, near Roche.

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near St. Austle, and of another tor (the name of which I have lost), overtopping the upper road, which leads to Buckland on the Moor. If my memory does not fail me, I observed it on a scale equally large in more than one other spot on the Cornish Downs, and on Dartmoor; but I either neglected to mark at the time, or have since mislaid the exact localities. I would venture to recommend to the examination of future tourists two points connected with this rock.

1. Whether some other of the tors on the confines of the granitic tracts (besides those specified) do not consist of shorl rock. From its external configuration and neighbourhood to the granite, it may be easily confounded with that rock until examined more closely.

2. Is it possible from the careful examination of the country surrounding Roche Rocks, to ascertain whether that remarkable eminence has been produced by the disintegration and washing away of some less durable beds which once enveloped it? or whether it may be regarded as an original inequality of surface ?*

Most of the varieties of external appearance produced in this rock by the different modes of aggregation, have been enumerated by Mr. Sedgwick (p. 18). To his list, I am enabled to add, as Nos. 5 and 6,

5. Alternate layers generally of great tenuity, of very minutely granular quartz and shorl, having all the aspect of a stratified

6. Real or pseudo breccia consisting of small patches of compact shorl imbedded in quartz, or vice versâ of quartz imbedded in shorl.

These varieties occur in the neighbourhood of the crystalline and more predominant form. No. 5 appears to offer another exemplication of a law, which I believe to obtain pretty generally, “ that crystalline rocks when they occur in large masses are most usually accompanied by schistose rocks composed of the same mineral ingredients in a state of greater alternation.” To the verification of this law, I would venture to solicit the attention of those who join a knowledge of mineralogy, and chemistry to that of geology. The establishment of its probability might lead to some important theoretical results. Nor should I omit to mention, that the varieties of shorl rock above noticed are peculiarly interesting from the examples which they afford, even in hand specimens, of the various phenomena of configuration incident to rocks of the schistose character. The marked distinction of colour and aspect existing between the two constituents (tourmaline and quartz) render these very striking and intelligible. Even the very small collection which I possess myself, offers within the scale of a few inches highly instructive examples of contortion, dislocation, crossing, and

* I would suggest a like examination of two singularly insulated masses of rock occupying opposite sides of a ravine near Camelford, known by the name of the Devil's

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heaving of veins. Neither this, however, nor my observations, are sufficiently extensive to justify the theorizing, with any confidence, on the subject. As far as I can conjecture, the appearances offered by my own specimens would be most readily accounted for by an hypothesis which should admit, 1. That the laminated arrangement of the rock is not in all cases the result of successive depositions. 2. That disturbances have taken place subsequently to the formation and contortion (if these be not synchronous) of the laminæ. 3. That at the period of these disturbances, the degree of consolidation varied in different portions of the mass. I would, however, conclude by strongly recommending this rock to the more accurate examination of · future travellers; and am, dear Sir, very truly yours,

J. J. CONYBEARE.

.

ARTICLE VI.

IIA

ARTICLE

On Hatchetine. By the Rev. J. J. Conybeare, MGS.

(To the Editor of the Annals of Philosophy.) MY DEAR SIR,

Bath Easton, Fcb. 10, 1823. I HASTEN to acknowledge that a perusal of Mr. Brande's elementary work on Chemistry (which has only of late fallen into my hands), has shown me that I have been anticipated by that gentleman in the examination of the mineral substance which I ventured to name hatchetine, and which is enumerated by him under the varieties of bitumen, as mineral adipocire. Mr. Brande's work was published, I believe, early in 1821. My own experiments, made the autumn before, were transcribed for the Annals in the January of that year. Strictly, therefore, I have to apologize to your readers only for the second of my communications (the short note appended to the examination of mumia), which an earlier perusal of Mr. Brande's work would certainly have caused me to suppress. Allow me to express my satisfaction, that the examination of the substance in question has fallen into better hands than my own; and that my opinion as to its specific difference from every other known variety of bitumen is corroborated by so competent an authority. With Mr. Brande's permission, however, I would still contend for the superior propriety of the name hatchetine, both for the reason formerly assigned, and from the feeling that it is rather desirable to banish from our nomenclature all such significant names as are not indicative of some actual property of the substance to which they are applied. Believe me, dear Sir, very truly yours,

J.J. CONYBEARE.

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Results of a Meteorological Register kept at New Malton, Yorkshire, in the Year 1822. By Mr. J. Stockton.

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BAROMETER.

1822.

Maximum.

Minimum.

Spaces described

in inches and parts.

Range.

Mean.

January
February
March.
April..
May
June
· July
August
September.
October..
November.
December.

30:27 29:10 29.870 1:17
30:70 28.25 29.784 2.45
30:30 28.80 29.687 1:50
30:34 28.95 29.720 1.39
30-35 29-30 29.857 1.05
30.17 29:50 29.938 0.67
29.87 29.10|29.514 0.77
30:10 29.02 29.616 1.08
30.20 29.09 29.764 2:11
29.90 28.92 29:396 0.98
30.06 28:51 29.360 1:55
30.65/ 28.05 29.935 2.60

6:38
11.69
10.13
5.50
5.73
4.64
5.71
4.89
5.76
7.21
8.58
9.63

Annual means, &r. 30:701 28.05 29.703 2.65

85.85

195

84

25

148.901

59

32

51

23

25 141194 39 26 34 48127 125

5

8 37.10

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