FOOTNOTES:
[123] Before his departure upon this excursion, we recommend him to examine the very instructive suite of specimens which were collected, and deposited in the Cabinet at Penzance by Mr. Ashhurst Majendie, a gentleman whose geological labours in this country are well known, and whose zeal and ability so greatly promoted the early advancement of our Geological Society. This valuable series has been greatly augmented by a Collection since presented to the Society by The Reverend John Rogers. The Geological tourist ought at the same time to make himself acquainted with the observations of Mr. Majendie "On the Lizard District," in the first volume of the Transactions of the Royal Geological Society of Cornwall; and those of Mr. Professor Sedgwick, on the same subject, in the Transactions of the Cambridge Philosophical Society.
[124] In the Greeb-rock, an insulated mass of greenstone in the sea beneath, there is a vein of Asbestus-Actynolite, mixed with Axinite, from four to twelve inches wide. This is a curious spot, well worthy the attention of the geologist.
[125] As will appear on the perusal of the first edition of this little work.
[126] A violin is in some parts of Cornwall called a Crowd, whence doubtless the name of Crowdero, the fiddler in Hudibras.
[127] The ancient name of Helston. The modern apellation is derived from a huge block of Granite which may be seen in the yard of the Angel Inn—Hellas-stone, or Helston.
[128] On the physical structure of the Lizard district, by the Rev. A. Sedgwick.
[129] The same relative position of these rocks may also be observed at Cadgwith, an interesting part of the coast north-east of the Lizard Point, and which we shall have occasion to notice hereafter.
[130] Sir H. Davy, in a paper on the Geology of Cornwall, published in the first volume of our Transactions, observes that "the nature and origin of the veins of Steatite in Serpentine are curious subjects of inquiry. Were they originally crystallized, and the result of chemical deposition? Or have they been, as for the most part they are now found, mere mechanical deposites, I am inclined to the last opinion. The Felspar in Serpentine is very liable to decompose, probably from the action of Carbonic acid and water on its Alkaline, Calcareous, and Magnesian elements; and its parts washed down by water, and deposited in the chasms of the rocks, would necessarily gain that kind of loose aggregation belonging to Steatite."
[131] It might on this account be worth while for the Glass-maker to try the effects of a small mixture of Steatite with the materials of which he makes his large crucibles, in order to prevent that great degree of shrinking to which they are now so liable.
[132] The quantity of air thus separated from water is so great that in the Alps and in the Pyrennees, very powerful bellows are made for forges by the fall of a column of water, through a wooden pipe, into a closed cask, in which it dashes on a stone in the bottom, when the air thus disengaged from it is carried by another pipe placed in the cover of the cask into the foundery.
[133] This substance presents with great distinctness those characters which distinguish it from Hornblende, viz. inferior hardness, difficult fusibility into a green enamel, and peculiar cleavage which discovers a considerable lustre in one direction which is entirely absent in the other; whereas Hornblende has natural joints of the same lustre in two directions.
[134] Mr. Majendie presented some of these specimens to Abbe Haüy, and compared them with those in the cabinet of that illustrious mineralogist, which were brought from the hill of Mussinet near Turin. M. Haüy observed upon this occasion, that the Coverack Specimens did not consist of pure Diallage, but that fibres of common Hornblende interrupted its texture. That of Mussinet is foliated, and has no such intermixture.
[135] For a long period this was considered as the only Cornish habitat of this mineral; but Dr. Paris subsequently identified its presence in a sand brought from a stream near the house of Colonel Sandys at Lanarth. See "Transactions of the Royal Geological Society of Cornwall." Vol. I. p, 226.
[136] See a History of this curious discovery in "A Memoir on the Life and Scientific Labours of the Rev. William Gregor, by J. A. Paris, M. D."—London, 1818.