A Letter from Mr. Moreton Gilks, F. R. S. to Dr. Mortimer, Sec. R. S. Giving Some Account of the Petrefactions Near Mat-Lock Baths in Derbyshire; With His Con-Jectures concerning Petrefaction in General

or upwards. He told me, he believed the Stone had been growing there for near thirty Years; but never apprehended it to be a Stone, but used to complain of a Weight, as if it were half a Pound, carried between his Legs. John Sisley, Surgeon and Apothecary, Town-Malling, Kent. XVII. A Letter from Mr. Moreton Gilks, F. R. S. to Dr. Mortimer, Sec. R. S. giving some Account of the Petrefactions near Matlock Baths in Derbyshire; with his Conjectures concerning Petrefaction in General. SIR, In the mountainous Part of Derbyshire, about Cromford, is a Valley of at least a Mile and half long, walled on each Side with high craggy Rocks; the East Side cliffy, the West more reclining, but extremely rough and difficult of Ascent; being composed of large loose Pieces of the Lime-stone Rock, of five, ten, or twenty Ton Weight; that seem at some Distance of Time to have broken off from the Top of the Cliffs, and fallen down into the Valleys.—At the Bottom of the Valley, which seems to be a great gaping Fissure of the Rock, runs the River Derwent harshly along its rocky Bottom. About the Middle of the Valley, at near 50 Foot perpendicular Height from the River, issue forth several Ri- Rivulets of a luke-warm Water, that pour themselves into the Derwent below. Some of this Water, being collected in a Reservoir, on account of its agreeable Warmth, hath of late Years been much used for bathing, and is called Matlock Bath. Now for about the Compass of 500 or 600 Yards, near to where this Water gushes out, the Stone appears of a very different Texture and Complexion; and proves, upon Examination, to be a perfect Incrustation, formed upon the original Rock; composing a factitious Stone, of Earth, Vegetables, &c. of various Kinds, such as usually grow in rocky Places, as Polypody, Tricomanes, and other Species of the capillary Tribe, Mosses, Brambles, Ivy, Hazle, &c.—There are several large Grotto's at about 15 Foot above the Level of the River, lined most curiously with the Stalactite, Lapidus Stillatitii, &c. Some of them nearly resemble large Bunches of Grapes, and other Clusters of Fruit, very beautiful to look upon. Specimens of most of them I think I have sent.—I found upon Examination, that the farther you penetrate into this Mountain, the closer and more compact the Stone appears; the Interstices in the petrified Matter being at the Depth of 15 or 16 Foot, almost filled up, and nearly as solid as the Lime-stone, of which the original Rock is composed; and even within four or five Foot of the Surface, though very open and porous; yet is it so hard as to be used in the Building about the Bath; and I imagine it may be equally durable, though easier to work with the Saw, than the close Lime-stone. The Mountain in several Places jets out almost over the Brink of the River; under these Protuberances are are the Grotto's, very dangerous and difficult to get at. It was here the Specimens I send you were collected †, but it is impossible to give you an Idea of the natural Beauty of the Place. The Frost-work, and incrusted Plants, are some of them so very delicate and tender, as to make it impracticable to bring them away with half their Beauty, by the most careful Conveyance. In one Place there is an Ivy creeping along the Rock, part of it entirely petrified, another part only incrusted, and a third still vegetating. In another Place is a Hazle-tree, the Root whereof composes a Part of this petrified Mountain, the Branches some petrified, and some tenderly incrusted. As these are changed, others spring up, and in Time will undergo the same Fate. In short, nothing in Nature can give a more clear Idea, or more beautiful Representation, of the whole Business of Petrefaction, than a curious Observer will see, and frame in his Mind from this Mountain. He will see, that not only the Water, as it distils out of the Rocks, is capable of incrusting and petrifying the Bodies it meets with in its Passage, but that even the Steams and Exhalations*, being highly saturated with these mineral Particles, will work the same Effect; as is evident in the Place under Consideration, and will generally best account for the Supply of petrifying Matter, brought to fill up the Vacuities that are left by the Decay and Waste of Vegetables incrusted over; and which, he will see, are in Course of Time constantly filled therewith. For although the Water of some † They are deposited in the Museum of the Royal Society. * Vide Woodward's Natural History, p. 136. 209. Springs Springs may be so loaded with mineral Matter, as, perhaps by penetrating the Pores of Wood and other lax Bodies, to increase greatly their specific Gravities; yet surely it is contrary to the Laws of Matter, and absurd to say, there is any hidden Property in such Waters capable of changing the Parts of one Body into another Body specifically different. It may in time, no doubt, lose its Texture and Coherency, by the Admittance of heterogeneous Particles of different Attractions; but the Cause of Coherency in the Parts of the original Body must entirely cease, and be dissolved, before it can be said to become a Part of any other Body whatever. Afterwards, indeed, the Space that was possessed by the Parts of the original Body, may be supplied by those of the new one, so as to make in time a uniform Stone in the Shape of the original Plant: But if this petrified Plant be still kept in the Place where the same petrifying Quality continues to act upon it, it will lose even that Shape, and become a Part of the Body it is contiguous to; and so a great many of these petrified Plants, and other Bodies united together, will compose large Masses and whole Strata of Stone. This is clearly the Case in the Instance now before us, and perhaps it might be carried so far as to strengthen our Conception about the general Formation of the Strata of Lime-stone or Marble; that appearing to be every-where, (notwithstanding Dr. Woodward dispatches them much more expeditiously *) but especially in the Peak of Derbyshire, such a Petrefaction as I * Woodward's Natural History, Part II Conf. 4. have been describing, quite finished. I could urge many Reasons for my Supposition, but I will not trouble you with them here, the Compass of this Letter not permitting me; nor do I know how far such Conjectures are capable of being used, with regard to the received Opinion of the World's Age; but if we had as good Authority to suppose it 60,000 Years old, as we have 6000, it would be worth the while to trace the Origin and Source of these petrifying Exhalations a little deeper than seems to have been done by Dr. Woodward; and might either perfect his History, or produce a more rational System of the Earth than has yet appeared. You will find, amongst the things I send, some Land-coral found in a Lime-pit, where is a great Quantity of it, between Two Strata of Lime-stone of at least Three Foot thick. You will find also some few Pieces of Pseudo-sapphirus, and other kinds of Spar; they are such as I picked out of the Fissures of the Rocks I have been describing. There is a vast Variety of these things in the Peak, much greater than hath been taken Notice of by any one; as I shall convince the Royal Society, when I am able to present them with a complete Collection of Derbyshire Fossils, in which I have already made some Progress: Who am, SIR, Burton, Nov. 26. 1735. Your most humble Servant, Moreton Gilks. XVIII. Part