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XI. On a remarkable deposit of Natron found in cavities in the Tower of Stoke Church, in the Parish of Hartland, in Devonshire.

BY EDWARD DANIEL CLARKE, LL.D.

LATE FELLOW AND TUTOR OF JESUS COLLEGE; PROFESSOR OF MINERALOGY
IN THE UNIVERSITY OF CAMBRIDGE; LIBRARIAN OF THE UNIVERSITY;

MEMBER OF THE ROYAL ACADEMY OF SCIENCES AT BERLIN;
HONORARY MEMBER OF THE GEOLOGICAL SOCIETIES OF
LONDON, EDINBURGH, CORNWALL,

&c. &c.

[Read November 27, 1820.]

IN the Chemistry of Nature, the mutual decomposition of bodies, by their action on each other, and the new synthetical results which follow this analysis, may be justly deemed among the most interesting phenomena offered to our view; and they are, perhaps, never more strikingly developed than in the formation of the native Salts, when they are found efflorescing and crystallizing upon the surface, and in the interstices, of minerals, which did not originally contain them. It has often happened to me to point out these changes, in my public lectures, to the University, and to call the attention of mineralogical Students to the operation whereby in a successive series of analysis and synthesis the eternal energies of the creative agency are continually manifested. To the attentive observer of Natural Chemistry, these phenomena are highly important; because, while they are calculated to illustrate

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the origin of some of the most remarkable substances in Nature, their consideration fills the mind with astonishing ideas of the activity, and renovating powers of that ceaseless Cause, which ordains new and beautiful forms, out of the decay and ruin of pre-existent beings. Many such phenomena might be here enumerated; but for the present I shall confine myself to one; namely, to the formation of native natron; under circumstances which were communicated to me by Dr. WAVELL of Devonshire; so well known to the scientific world by his former discovery of the phosphate of alumina; called, in honour of him, by the name of Wavellite.

Dr. WAVELL transmitted to me a small parcel of a white salt, which he had lately found in the Tower of Stoke Church, in the Parish of Hartland, in Devonshire; desiring me to examine it. The description of the manner in which it was deposited, shall be given from the letter which accompanied this alkaline substance, in his own words." Many of the stones, in the interior of the tower, were hollowed out, and the cavities nearly filled with the Salt. Upon other stones there was merely an efflorescence. Some of the cavities were only large enough to admit my hand; others would nearly receive my head. I send you a small fragment of the stone, which I broke off with difficulty; for although the stones appear much decayed, they are very hard."

The stone in question, is evidently a slate-coloured sandstone; but unlike any sandstone I had before seen. Perhaps it is nearly allied to the Graiiwacke of the Germans, but of a purer siliceous nature. The grains of sand are so minute, and withal so intimately aggregated, as to be imperceptible to the naked eye. It préserves its colour when first acted upon by the common blowpipe; but when wrapped in platinum foil, and exposed for half an hour to a white heat in a coal fire, its colour becomes reddish white. Exceedingly minute particles of silvery mica may then be discerned

with a lens. The action of heat produces hardly any magnetic property; the smallest particles being scarcely affected by the magnet afterwards. Its specific gravity equals 2.625, which alone proves it to be nearly pure silica; the specific gravity of Quartz being i 2.6. It scintillates freely with steel. Placed in dilute muriatic acid it yields no effervescence; but the acid being boiled, causes it to exhibit an almost imperceptible effervescence. The same acid being afterwards evaporated to dryness, and distilled water added, oxalate of ammonia detected a trace of lime. Carbonate of soda also threw down carbonate of lime from the same solution, but with a beautiful reddish hue owing to the precipitation also of oxide of iron by means of the alkaline body. Hence it is manifest that some carbonate of lime had existed in this sandstone; probably as a cement; but the stone having been corroded and decomposed in the formation of the salt, I thought it right to see if any carbonate of lime existed in the salt itself, which proved to be the case; and this I ascertained in the following manner.

I dissolved a portion of the salt in distilled water; decanting the supernatant solution so long as it continued to change the blue tincture of vegetables to a green colour. When all action upon the vegetable tincture had ceased, and the insoluble residue had been repeatedly washed with many volumes of distilled water, I poured upon it some muriatic acid; when a visible and somewhat violent effervescence ensued; particles of the effervescing body being carried up and down in the liquid. That these particles were carbonate of lime is evident from this circumstance; that the acid being now decanted into a filter and collected in a watch-glass, and evaporated to dryness, and distilled water added, the presence of lime was fully attested by oxalate of ammonia.

My attention was now given more immediately to the salt itself; in the examination of which I proceeded as follows:

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