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minerals have also been found in it; viz. axinite, garnet, topaz, &c. Are not these some of the strongest marks of a primitive rock? Some specimens of it were sent by a member of our Society to Werner, who recognized in them the clayslate of Saxony.
"That greywacke exists, and abounds in some parts of Cornwall, will not be denied; but I apprehend it is not to be found, except in small and scattered portions, in that part in which nearly all the tin and copper mines are wrought. It appears to commence near Grampound, and to extend westward about three miles from Truro: how far southward, I have not been able to ascertain. Its extent northward in mass is probably not from Truro; but it is found in bunches as far as Padstow, and Tintagel Castle. Near the former place, it is highly characterized; and at Tintagel impressions have been found in it. The lead veins of the Garres, and those of Pentire Glaze, and the vein of antimony at Huel Boys, are probably in greywacke; but I have never seen either copper or tin in greywacke, nor am I aware of any tin veins which intersect it."
VI. Observations on the Submersion of Part of the Mount's Bay, and on the Inundation of Marine Sand on the north Coast of Cornwall. By Henry Boase, Esq. Treasurer GSC.
In this paper, Mr. Boase first examines and refutes the tradition handed down by the historians of Cornwall, respecting the submersion of the country called Lionnesse : he then discusses that which relates to an irruption of the sea over a tract of low woodland, now forming the northern part of the Mount's Bay, showing that it is strongly corroborated by the geological indications of the district; and he concludes with an account of the overwhelming at an unknown period, by an immense inundation of sea-sand, of a considerable tract of cultivated land on the northern coast of the county.
VII. On the Nomenclature of the Cornish Rocks. By John Hawkins, Esq. FRS. &c. Hon. MGSC.
This communication commences with some remarks on the benefits conferred by Werner on the sciences of geology and mineralogy, which are succeeded by observations on the use of the term greywacke, in which the author suggests that the substance so denominated should be considered only as a subordinate formation to clayslate.
The characteristic appellations given by Werner to some of the specimens in a collection of the principal Cornish rocks, transmitted to him by Mr. Hawkins, form the next subjects of the paper, and it terminates with some reflections arising from the consideration of them.
VIII. On the Temperature of Mines. By John Forbes, MD. Hon. Mem. and late Sec. GSC.
IX. Observations on the Hornblende Formation in the Parish of St. Clere. By the Rev. John Rogers, MGSC.
The local details of which this paper consists are not susceptible of abridgment; but it contains the following analysis of the serpentine of Clickertor, by the late Mr. Gregor, which, we believe, has not hitherto been given to the public:
X. On the Phenomena of Intersected Lodes, and the legitimate Inferences which may be drawn from them; and
XI. On the Intersection of Lodes in the Direction of their Dip or Underlie. By John Hawkins, Esq. FRS. &c. Hon. MGSC. These interesting papers cannot usefully be epitomized.
XII. On the Geology of the Land's End District. By John Forbes, MD. Hon. Mem. and late Sec. GSC.
We have only room for a brief general sketch of the subject of this memoir, the physical structure of that portion of Cornwall situated to the westward of a line drawn from the estuary of Hayle, on the north coast, to Cuddan Point on the south, which Dr. Forbes calls, for the sake of distinction, the Land's End district. "The geological structure of this district," he observes, "may be said to be very simple, inasmuch as it includes but a small number of rocks, and as the various relations of these to each other are very similar and readily discoverable. The main body of the district is granite,--a rock which indeed constitutes nine-tenths of the whole. On the edges of the granite, in different points of the coast, reposes a certain assemblage of rocks, which, from their intimate relations, obviously constitute one formation. These rocks I shall take the liberty of naming in this paper the slate formation; a term which answers exactly to the killas country of the miners and farmers in this part of the county. Generally speaking then, this district consists of two, and only two formations; the granite formation, and the slate formation; very dissimilar in appearance, and indeed very distinct in all their characters; although, as will hereafter be more particularly noticed, in all probability of contemporaneous origin."
"The granite, generally speaking, is large-grained, and very frequently possesses that particular arrangement of the crystals of felspar that entitles it to the epithet porphyritic. This character may indeed be said to be almost universal, and is exemplified in the pillars of almost every field gate.......Almost the only foreign ingredient (with the exception of the metallic ores in the neighbourhood of some veins and floors of tinstone), con
tained in the granite of this district is shorl. This occurs in great plenty. In one spot, on the coast near Cape Cornwall, of several hundred yards in extent, this mineral forms so considerable a proportion of the rock, as to give it quite a new aspect, and has indeed procured it from geologists a distinct appellation, viz. short-rock......The locality now mentioned, and the celebrated Roach Rock, in the neighbourhood of Bodmin, are the only places in Cornwall where I have heard of this modification of granite being found in mass. In the form of veins, indeed, traversing both the granite and slate at their junction, it is very
The slate formation, "is much more complicated than the last, and affords much greater scope for geological research. It comprehends, as far as I have been able to ascertain, five distinct rocks. These are clayslate, hornblende rock, greenstone, compact felspar, and slaty felspar.......By felspar rock, I mean a rock of small granular structure, consisting, apparently, principally, or almost wholly, of felspar. By slaty felspar, I mean a rock apparently of the same composition, or only with the addition of a very small portion of mica, with a distinct slaty fracture. These five rocks, constituting the assemblage to which I have given the name of the slate formation, occur in beds of various magnitude, alternating with each other; but with one very small exception, I have uniformly found the slaty felspar rock in immediate contact with the granite; and I think it not improbable that in proportion as we recede from this central rock, we shall find the slaty felspar become less frequent, and be finally superseded by some of the varieties of clayslate. "The rock which I have named compact felspar, which consists principally, I believe, of compact felspar with a little quartz, I have so named in deference to my excellent and learned friend Prof. Jameson: it may, however, be considered as a variety of greenstone. The only difference between it and common greenstone, is its containing a more minute portion of hornblende, and being, consequently, of a lighter colour than that rock generally is." The author has presented to the Society specimens of every rock which he has described.
XIII. An Account of the Alluvial Depositions at Sandrycock. By the late Philip Rashleigh, Esq.*
The alluvial beds described in this communication are very similar to those at the stream-work of Poth, of which an account was long since given by Mr. Rashleigh, at the end of his work entitled "Specimens of British Minerals."
XIV. Observations on the Alluvial Strata at Poth, Sandrycock, and Pentuan. By John Hawkins, Esq. FRS. &c. Hon. Mem. GSC.
These observations will not admit of profitable abridgment.
* Drawn up in 1797, and communicated by John Hawkins, Esq. Sept. 1819.
XV. On the Mineral Productions, and the Geology of the Parish of St. Just. By Joseph Carne, Esq. FRS. &c. MGSC.
The space to which our analysis must be confined obliges us to pass over Mr. Carne's enumeration of the minerals which have been discovered in this district, together with the greater part of his description of the peculiar geological facts observed in it: the only sections of the latter for which we have room are the following:
"Floors, or Horizontal Beds.-St. Just abounds in floors of tin, more than any other part of Cornwall.
"In that part of the tenement of Trewellard which is in a slate country, some tin floors have been wrought near the surface; the deepest is only seven fathoms below it: they were from one to two feet in thickness, and perhaps twenty feet in diameter; they occurred at the junction of several tin lodes.
In Huel St. Just, a mass of tin ore, of a very singular nature, was discovered some years ago, which appears to belong to the floor formation. It first appeared at the depth of 17 fathoms under the sea, and has been followed downwards about 10 fathoms. It was seven or eight feet in diameter. At the top, it was on the south-western side of the tin lode; but it inclined in a very small degree, until it was almost wholly on the northeastern side of the lode. The cavity in which it was found, had the appearance (after the tin was taken away) of a large underlying shaft, closed at the top. The most remarkable circum stance, however, relates to the state in which the tin ore was found; instead of being in a solid body, as is usual in floors, it appeared (as the miners termed it, from whom I received the account) like a heap of attle, or rubbish; just as if it had been thrown in that state into the cavity. The fragments were not rounded, but had all the appearance of the broken tinstone, which is generally seen on the surface of tin mines. The top of this mass of ore was about three feet below the granite top of the cavity, as if it had sunk by contraction or pressure. One of the miners told me that he found sufficient space between the granite covering and the ore, to sit upright on the latter. In its present deepest part, it is not so wide as it was at a higher level; but it is more compact. The tin ore, as raised from this cavity, contained, according to the miners' mode of calculation, from 700 to 1000 of tin to every 100 sacks. This floor, although of far greater thickness than any other which has yet been discovered, does not appear to be the result of the union of several lodes, for no such union takes place near it. Only one lode has been found connected with it, which, although perfectly distinct in the granite, both south-east and north-west of the floor, appears to lose its individual character, and to form one
"It must not be supposed from this description that the floors are round: on the contrary, they are frequently very irregular, but their surface is about as large as would be comprised in a circle of 20 feet diameter."
New Series, VOL. VI.
body with it at the meeting. The floor, therefore, probably belongs to the same formation as the lode."
"Botallack is, however, the principal locality of the floors. Here they have been discovered, first, in slate. There is only one floor wholly in slate, which is 36 fathoms under the sea. It is about a foot thick, and occupies the space between a side lode and a neighbouring master lode, which is from 12 to 18 feet. No junction of lodes takes place at this spot. They occur, secondly, between the slate and the granite. Here, in a part of the mine called the Bunny, the principal floors have been found. The highest floor was so shallow as to be level with the surface, and tradition reports it to have been discovered by some of the tinstone having been kicked up by horses going over it: to this succeeded a floor of the country from one to three feet thick: then followed a second floor of tin, under which was found another floor of the country; and in this manner no less than seven floors of tin succeeded each other: the thickness of each was from six to twelve feet; some of them were full forty feet in diameter, but in general they were not so large. The country between the floors was generally slate, although they occurred just at the junction of the slate and the granite. At this spot there is a union of several lodes. It is singular that one of the marks by which the miners knew they were approaching a floor of tin, was their meeting with a floor of tourmaline, to use their own expression, the cockle rode on the tin.' Wherever they discovered the tourmaline, they were confident of finding a floor of tin under it. The tourmaline was accompanied by chalcedony, and I have seen veins of chalcedony running through it. Thirdly, in granite. In another part of Botallack, there are no less than 10 floors of tin, each as large as a space of about 30 feet square, succeeding each other in the same way as those which have been already described. The first was very little below the surface: the last is about 36 fathoms deep: they are from six to twelve feet thick. The agents of Botallack have assured me, that although these floors appear to be connected with one of the tin lodes, there is no junction of lodes in the space where they occur. In other parts of this mine, solitary floors have been found at different depths, on one of which, at 22 fathoms under the surface, the miners are now at work. It is about nine feet in diameter, and nearly round. They have seen its extent, and have found the country both above and below it (for it is quite horizontal) to consist of a very hard granite rock,"
"These floors have generally been regarded as the result of the union of several lodes. This, however, is cutting a knot which is not easy to untie. As some floors have been discovered where no union of lodes has taken place, such a union does not appear absolutely necessary to their formation. In the case of a single floor of tin, not larger than those which have been