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2. M. paniculata, foliis oblongis obtusis pinnatifidis ciliatis, perianthii fauce dilatatâ, coronâ simplict acutè dentatâ.

Gynopleura linearifolia, Cav. Icon. iv. p. 52. t. $76. ?

HAB. In Chili boreali.—Alexander Caldcleugh. ħ. (v. s. in Herb. Lamb.)

Planta erecta, pyramidato-ramosissima, leviter canescens, 3-4-pedalis. Rami teretes, pube subtili vestiti. Folia alterna, sessilia, nunc basi auriculatà amplexicaulia, oblonga v. lanceolata, obtusa, pinnatifida, pube sericeâ pilis plurimis setaceis intermixtâ potissimùm ad margines ornata, uninervia, nervo pinnatè ramoso, patentia, semipollicem v. pollicem longa, et 3 lineas v. semiunciam lata; ultima lineari-oblonga, sæpe integra: laciniis oblongis obtusissimis; infimis duabus majoribus, stipulas simulantibus. Flores paniculæ modo dispositi, numerosissimi, pallidè lutei, siccitate violacei! pedicello brevissimo crasso suffulti. Perianthium copiosè villosum, unciale: tubus angustus, cylindraceus, imâ basi callosâ: faux dilatata, campanulata, tubo duplò triplòve longior: corona simplici, tenuissimè membranaceâ, multidentatâ, dentibus brevibus acutis inæqualibus, è nervorum calycinorum ramis lateralibus arcuatis ortum ducente: limbus duplici ordine 10-partitus, uterque persistens, coloratus; laciniis exterioribus calycinis, lanceolatis, obtusis, æstivatione imbricatis; interioribus petaloideis, alternantibus, ovato-lanceolatis, mucronulatis, lateribus parum inæqualibus, magis coloratis, æstivatione convoluto-imbricatis, basi aliquanto attenuatis. Nervi perianthi adhuc simplices, ad summitatem tubi in ramos tres divisi; alternis ramulo intermedio in laciniis petaloideis ramosissime diffuso; calycinarum laciniarum ramulis lateralibus brevissimè distinctis, arcuatis, cæterùm confluentibus. Cætera ut in ordine.

For numerous specimens, both in flower and fruit, of this curious species, we are indebted to our highly valued friend Alexander Caldcleugh, Esq. F. R. S. & F. L. S. whose zeal in the cause of science is known and appreciated. He discovered it in the neighbourhood of Coquimbo in Chili, together with many other new and equally interesting plants, a complete collection of which he has transmitted to Mr Lambert. It may possibly prove to be the same with the plant of Cavanilles above quoted, notwithstanding the discrepancies in the description and figure; but, as I have never seen specimens of it to compare, I dare not venture to affirm them to be identical.

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Account of a Gelatinous Quartz or Siliceous Sinter, which" forms the basis of varieties of Old Red Sandstone. By M. T. GUILLEMIN.

As this interesting mineral occurs in some of the sandstone of this country, we have drawn up the following account from a memoir of Guillemin, published in the Annales des Mines for 1826.

External Characters.-This mineral is of a pretty pure white colour, which, in some varieties, passes into greyish or yellowish white; it has a resinous or semiresinous lustre, and passes into dull; it presents itself in irregular masses; its fracture is sometimes conchoidal, sometimes subconchoidal or even; it is scarcely translucid on the edges; when dull, it is opaque; it scratches glass with difficulty, and is scratched by steel; it is easily frangible; it adheres to the tongue, and is capable of absorbing a large quantity of water; its specific gravity varies according to the quantity of liquid which it contains,

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When immersed in distilled water, gaseous bubbles are speedily disengaged, which rise after one another; and, at very short intervals, a, whizzing noise is emitted, and from time to time cracks are heard; a fissure then forms, and gives rise to a new column of bubbles. At the end of twelves hours, there are still bubbles escaping; after eighteen hours the absorption appears complete. If boiling water be used, the disengagement is much more rapid, and by means of it bubbles are still made to rise from a fragment that has been immersed in cold water for several hours, and which appears saturated. A fragment of about five grammes weight, already containing 11.11 per cent. of water, according to a trial made at the moment, still absorbed 14.36, in all 25.47 per cent. at the temperature of six degrees of the centigrade thermometer. A hundred parts of this substance, therefore, saturated with water, contain 20.30. Another fragment of about 10 grammes, dried before immersion, absorbed 24.51 per cent. of water at zero, or about a fourth of its weight, as in the preceding experiment.

These specimens, left to themselves for two or three hours,

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returned to their original state, that is to say, came to contain only 11 or 12 per cent. of water.

The density of a fragment saturated with water was 1.80 at 6 degrees, 1.812 at 6 degrees, 1.797 at 13 degrees; that of a fragment containing 0.111 of water, 1.67 at 2 degrees; and that of a dried fragment 1.53 at 5 degrees. In the two last experiments, the absorption of water, and the 'disengagement of gases were prevented, by covering the surface of the fragments with a thin coat of olive oil. Lastly, the density of this substance, when weighed dry out of the water, and under the water, after an absorption of eighteen hours, was found to be 2.215 at 13 degrees of the centigrade thermometer.

Chemical Characters.-Exposed to the heat of a lamp in a small matrass, this mineral affords water; gently heated in a platina crucible, it gives out all its water without losing its resinous lustre; it becomes a little more translucent, with a tint of yellow opaline colour; when quickly heated, it decrepitates, splits, whitens, and becomes opaque by the intrusion of the air into the fissures which are formed.

It is infusible before the blowpipe. The thinnest splinters, when strongly heated, become transparent, and assume the vitreous lustre and hardness of hyaline quartz. It is affected, like pure silica, with all the chemical agents. Caustic potash in concentrated solution very readily attacks it at a boiling heat; it is dissolved almost instantaneously. Muriatic acid precipitates it in large white gelatinous flakes, when the liquor is concentrated; and, on the contrary, when a sufficient quantity of water is used, a precipitate is not immediately obtained, and by evaporation a transparent jelly is procured.

Analysis. The water is not combined in this siliceous substance. I thought, at first, that it was; having been deceived by the difficulty of chasing the last portions of this fluid, which is experienced when the heat of boiling water only is employed; but, I found, that, by a prolonged desiccation, the water always diminished, and at length was entirely expelled. The results of its analysis are the following:

JANUARY-MARCH 1827.

Y

[blocks in formation]

It contains no lime, nor have the oxides of iron or of manganeşe been detected in it. I have in vain searched for alkalies by means of carbonate of lead.

Observations.-This siliceous substance differs from the quartzes and flints in many of its characters, and especially in the density, which, in these minerals, is about 2.65; but it has a great resemblance to the siliceous sinter (Quartz concretîonné thermogène of Haüy). Both have the same lustre, the same! hardness, the some fracture. The density differs but little; Klaproth found that of the thermogenous quartz to be 1.807. These two minerals appear to be a siliceous jelly scarcely consolidated; they are both equally soluble in potash, and they have both the property of retaining water, and the power of absorbing a new dose of it. The difference which exists between these two substances is the manner in which they appear in naThe siliceous sinter or thermogenous quartz is almost always in stalactites or concretions in the neighbourhood of hot springs, particularly those of the Geysers in Iceland. A subspecies occurs in the island of Ischia, upon a decomposed granite, and is considered as a volcanic production *. The position" of the gelatinous quartz is different.

ture.

Geognostical and geographical positions.—It occurs in the Commune of Tortezais, in the Department of the Allier, and is very abundantly diffused there, sometimes serving as a cement to sandstones, and sometimes occurring in the midst of these sandstones, in masses often of considerable size. On the route from Noyant to Cosne, between Bussière and Tortezais, one of these masses is seen intersecting the road for a length of 30 metres, and recurring on each side in the fields in detached pieces over a great extent.

It is fissured in various directions, without any appearance of regularity. The surfaces exposed to the air are always more or less altered, and pass into floatstone (nectic quartz) I have not

been able to meet with it in the form of concretions.

If this

* Vide Jameson's System of Mineralogy, and Manual of Mineralogy.

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substance has been deposited by hot springs, they must have been very large and very numerous, and it would be astonishing should no remains of them be still visible. None of those which I saw were either saline, or warm, or incrusting. The nearest warm spring is that of Bourbon l'Archambault, and it does not form siliceous deposits.

The sandstones which contain this gelatinous quartz must have been deposited at the same time with itself, for they are intimately mixed. The gelatinous part always contains rounded grains of quartz, and it is rare that the sandstones have not this jelly, which serves as a cement to it, although it is only in small. quantity; and there is a transition from the one to the other by a change in the proportions of the rounded grains, and of the dissolved portion.

The variety of sandstone which abounds most in gelatinous silica, is formed of grains of hyaline and milk-white quartz, rounded, and of a small size; some grains of opal also are seen in it, but there is no felspar or kaolin. When the silica is in the nectic state, it is difficult to determine whether there be kaolin or not, from the mutual resemblance which these two white and friable substances possess. Another variety of sandstone, is, in a great measure, formed of grains of hyaline quartz; some scales of mica and spots of red oxides of iron are also perceived in it. The red spots are seen to increase in size and number; they are formed of a siliceous paste, coloured with tritoxide of iron. The red colour at length predominates, and the mass becomes entirely of that tint; a multitude of small grains of quartz and of gelatinous spots are, however, seen in it.

These sandstones are supported by conglomerates composed of blocks of quartz, granite and micaslate. These conglomerates rest immediately upon the primitive formations. Above the red-sandstones there occur strata of sandstone and bituminous slate, with impressions of ferns and junci, containing beds of black coal and iron-ore. They have the same direction and inclination as the coal-sandstones which they support. No rock of volcanic origin is found in all these formations. It is, therefore, in an intermediate deposit, which might be referred to the old red-sandstone, or the lower beds of a coal-formation, that

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