361 



LAVANDULA. 



LAYER. 



383 



mass. Trachyte, ono of the most prevalent of ail Tolcanio products, 

 consists chiefly of felspar (90 per cent), and includes almost every 

 conceivable modification between porphyry and obsidian. 



Basalt, another of the characteristic volcanic rocks, contains, besides 

 much felspar, a considerable admixture of augite or hornblende, and 

 is rich in oxide of iron, sometimes titaniferous. 



If lava were wholly felspathic it would consist principally of silica, 

 alumina, and potash, as in column 1, the average of seven analyses of 

 felspar : if wholly hornblendic, as in column 2, which expresses the 

 composition of hornblende from the Vogelsberg, according to Bons- 

 dorff ; if wholly augitic, as in column 3, which is the analysis of black 

 augite from ^tna by Vauquelin. 



(1.) () (3.) (4.) 



Silica . . 64-0 42-2 52-0 Sl'O 



Alumina . 18-9 13-9 3-3 19'0 



Lime . . 0-8 12'2 13'2 9'5 



Magnesia . 137 lO'O 



Potash .137 



Soda . . 4-0 



Oxide of Iron 0'8 14.6 147 14'5 



Ac. . . 6-8 



Th' fourth column gives, for comparison, the result of Dr. Ken- 

 nedy'* examination of the compact lava from Catania. Soda, an 

 ingredient of compact felspar, appears more frequent in lavas than 

 potash, which belongs to common felspar : magnesia is not common, 

 its place in the chemical aggregate being probably occupied by oxide 

 of iron. [AuoiTE.] 



Trachyte is conjectured by Dr. Daubeny to be derived from granite ; 

 and eome volcanic products present in their chemical composition a 

 remarkable analogy to that of granite. Obsidian, of which a specimen 

 from Hecla yielded to Vauquelin 



Silica 78-0 



Alumina lO'O 



Potash 6-0 



Lime O'l 



Soda 1-6 



Oxide of Iron I'O 



967 



is by the same writer spoken of as derived from trachyte. 



In comparison with this we may place the composition of granite 

 as calculated by Sir Henry de la Beche from its constituents, 

 namely : 



Silica 74-8 



Alumina 12'8 



Potash 75 



Lime <H 



Magnesia 1 - 



Oxide of Iron 1'9 



&c. 0-3 



987 



The certainty with which the mineral ingredients of lava can be 

 identified depends principally on the degree of crystallisation which 

 circumstances have permitted, and this on the rate of cooling and 

 pressure to which the melted masses have been subjected. There is 

 in lava every degree of variation, some specimens being of granitic, 

 and others of earthy, compact, resinous, or vitreous texture. Yet in 

 most cases the method of mechanical analysis proposed by Cordier 

 will determine, what very often a lens detects, the real mixture of 

 various minerals in what seems a homogeneous mass. According as 

 felspar or augite predominates, volcanic rocks have been classed, by 

 Cordier and most writers, as trachytic and basaltic. Mr. Scrope 

 {' Journal of the Royal Institution/ vol. xxi.) has proposed an inter- 

 mediate group to be called graystone. He states that in trachyte, 

 felspar (or its substitute) exists in the proportion of 90 per cent, and 

 upwards, in graystone more than 75 per cent., and in basalt leas than 

 75 per cent. The specific gravity of trachyte is about 27, of gray- 

 stone 3'0, of basalt even 3'5 ; differences which correspond with their 

 chemical composition. The colours yielded by these rocks, when 

 melted by the blow-pipe, afford a good test for the fine-grained sorts. 

 The glass from trachyte is light-coloured and nearly transparent ; 

 graystone gives a darker glass with green or black spots; basalt is 

 changed to a dark green or black enamel. According to conditions of 

 solidification, in water, in air, or in fissures of the earth, the 

 minerals which occur in lava are variously distributed so as to give it 

 porphyritic, amygdaloidal, or concretionary characters; and the 

 masses appear compact, porous, cellular, vesicular, cavernous, spumous, 

 or filamentous and all these circumstances are observable in glass 

 and other products of artificial heat, which are subject to unequal 

 rates of cooling and under different circumstances. I VOLCANO.] 



LAVANDULA, a genus of Plants belonging to the natural order 

 Lamiacea;. It has a tubular calyx nearly equal, 13- or rarely 15-ribbed, 

 shortly 5-toothed, with the 4 lower teeth nearly equal, or the 2 lower 

 narrower, the upper either but a little broader than the lateral ones, 

 or expanded into a dilated appendage ; the upper lip of the corolla 

 2-lobed, lower 3 lobed, all the divisions nearly equal, the throat 

 somewhat dilated ; stamens didynamous, diclinate. 



L. ipica is a native of the south of Europe, of which there are two 

 varieties, if not distinct species, termed L. latifolia and L. anyustifolia,. 

 The former is also called Spike Lavender, or simply Spike, and the oil 

 which it yields differs considerably from the oil of L. anyustifolia, or 

 L. vera, and is termed oil of spike, or foreign oil of lavender. This 

 sort is much less fragrant, of a deeper green colour than the oil of the 

 true lavender, and is merely used in painting, or to adulterate the 

 genuine oil, which is so extensively employed in the preparation of 

 perfumes. 



The flowers of the L. angvxtifolii, are the parts employed in 

 medicine. They should be collected before they are expanded, as 

 they are then possessed of a more powerful aromatic odour and a 

 hot bitterish taste. By distillation they yield an oil, which is yellowish, 

 but by rectification becomes nearly white. It has the agreeable 

 strong odour of lavender, and a burning bitterish taste. It is very 

 limpid, but becomes thicker by time. The specific gravity is variable; 

 that of the rectified oil is about 0'872. The freshly-rectified oil of 

 lavender acts on litmus paper, reddening it more powerfully than 

 when a year old. In the cold it deposits a lavender-camphor, or 

 stearopten. It is often adulterated by oil of turpentine and oil of 

 spike. The oil dropped on sugar relieves slight spasms of the stomach; 

 when diffused by alcohol in water it constitutes the spirits of laveuder. 

 The compound tincture of lavender is useful in similar cases, and is 

 the best means of covering the disagreeable taste of aloes. 



LAVATE'RA (in honour of the two Lavaters), a genus of Plants 

 belonging to the natural cruder Malvaceae. It has numerous styles, 

 a double calyx, the outer one being 3-leaved, the inner 5 leaved ; 

 the capsules orbicular and many-celled ; the cells circularly arranged, 

 and 1-seeded. 



L. arborea, Tree Mallow, has a wooded stem, the leaves 7-angled, 

 plaited, and downy ; the pedicels aggregate, axillary, 1-flowered, and 

 much shorter than the petiole. It is a native of Italy, Spain, Portugal, 

 the north of Africa, and the Canary Islands, on maritime rocks ; also 

 in Britain, in the Isle of Wight, on Portland Island, in Cornwall, 

 and Devonshire. It is the MoAoxn of Theophrastus ('Hist. PI..' 

 i. 5; i. 14). 



L. Neapolitana has an herbaceous scabrous erect stem, with 

 roundish 7-nerved leaves, and 7 blunt crenated lobes : the pedicels 

 axillary and aggregate, the involucel shorter than the calyx, the lobes 

 of the calyx acuminated. The flowers are blue with obcordate petals. 

 This species is a native of Naples, by the sea-side, and is much culti- 

 vated in our own gardens as an ornamental plant. 



L. Olbia has a shrubby stem, rather scabrous, from distant fascicles 

 of hairs ; the leaves are soft, woolly, 5-lobed, the upper ones 3-lobed, 

 with the middle lobe elongated ; the uppermost leaves are oblong, 

 almost undivided, the flowers solitary and sessile. It is a native of 

 Provence, in hedges about D'Hieres. 



None of the species of Lavatera are of any importance or value, 

 excepting as ornamental plants. Many of them are hardy, easily 

 cultivated, and well adapted for shrubberies. The greenhouse and 

 frame species will thrive well in a mixture of loam and peat, or 

 any light soil; they may be planted out during the summer 

 against a south wall, and if protected in the winter by a mat, will 

 generally survive throughout the year. The perennial species prow 

 in any kind of soil, and may be propagated either by dividing the 

 plants at the root or by seeds. The annual and biennial kinds should 

 be sown in the open border during the spring. The species chiefly 

 worth cultivation in gardens are L. Olbia, L. flava, L. unyuiculata, 

 L. Ntapolitana, L. Cretica, L. Lusitanica, and L. trimettrit. 



(Don, Dichlamydeous Plants ; Babington, Manual Brit. Sot. ; Fraas, 

 Sywpsit Pla.ntarv.rn Florae Clauiete.) 



LAVENDER. [LAVANDULA.] 



LAVENDULAN, a Mineral which occurs amorphous. Colour 

 lavender blue. Streak paler blue. Lustre greasy, inclining to 

 vitreous. Hardness 2'5 to 3'0. Occurs at Aunaberg in Saxony, with 

 cobalt and iron-ores. Accorning to Plattner, it contains arsenic, and 

 the oxides of cobalt, copper and nickel, and water. 



LAVER, a substance sometimes used as food, consists of the fronds 

 of marine plants belonging to the genera Porphyra and Ulv a. 



Purple Laver is furnished by Porphyra laciniata and P. vulyaris, two 

 species common on rocks and stones iu the sea on many parts of the 

 British coast. They derive their botanical name from their beautiful 

 purple or violet colour, which is produced entirely by the multitudes 

 of spores, arranged in twos, threes, or fours, with which the whole 

 frond is filled. 



Green Laver is the Viva, latissima, a very common plaut in the 

 sea on rocks and stones, not only in Great Britain, but also on the 

 coasts of India, Australia, the Cape of Good Hope, and South America. 

 According to Lightfoot, the Scottish Islanders ascribe to it anodyne 

 properties, and bind it about the temples to assuage the pain of 

 headache iu fevers, and to procure sleep. 



In the Western Isles of Scotland, we are informed by the same 

 authority, the inhabitants gather it in the month of March ; and after 

 pounding and stewing it with a little water, eat it with pepper, 

 vinegar, and butter; others stew it with leeks and onions. In 

 England Laver is usually stewed and rendered palatable with lemon- 

 juice; to many persons it is however nauseous, and it has been 

 suggested that its introduction to fashionable tables was the sly 



