CAI.CEDONY. 



CALIGUS. 



713 



bohedrons and 50 scalinohedrons have been distinguished. As might 

 naturally be expected, the combinations resulting from so large a 

 number of simple forma are exceedingly great, and Bournou, who has 

 written a treatise of three thick volumes on this mineral and Arra- 

 gonite, has distinguished no less than 700 varieties of form. Of these 

 154 are described in the large work by Hauy, accompanied by very 

 accurate drawings of each. 



A general knowledge of the crystalline form of this mineral may 

 however be easily obtained by acquiring a knowledge of the relation 

 of the faces of the five simple forms and the hexagonal prism referred 

 to above ; as in almost all the more ordinary combinations the general 

 feature of the crystal is produced by one of these. The fiy. 2, which, 

 as has been already stated, is considered as the ground-form, is a 

 rhombohedron, the faces of which are inclined to each other in the 

 terminal edges at 105 5'. This form, though exceedingly rare in pure 

 calcspar, is however the prevailing crystal in the nearly allied species 

 produced by the combinations of the carbonates of lime and magnesia, 

 as will be seen by referring to the article DOLOMITE. In deter- 

 mining the relations of any form, the position of the planes of this 

 rhombohedron in reference to the other parts must first be fixed, and 

 this is readily accomplished in every case, owing to cleavage-planes 

 running parallel to its faces. This being determined, all other rhom- 

 bohedrons are at once divided into rhombohedrons of the first order, 

 such as fiy. 4, which have their faces situated as the faces of the 

 ground-form, or into rhombohedrons of the second order, the faces 

 of which are situated as the edges of the ground-form, as is the case 

 with f'js. 1 and 3. 



The rhombohedron fig. 1, which may thus be seen to belong to the 

 second order, is readily recognised by having its faces y making the 

 same angle with the vertical axis A B (Jig. 2) as the terminal edges of 

 the ground-form, so that in a combination the terminal edge of the 

 ground-form is truncated by the plane y. This rhombohedron, which 

 is called the first obtuser, has the angles at the terminal edges 

 135 57', and has with the same breadth its vertical axis one-half 

 that of the ground-form. It ia one of the most common of the 

 rhombohedrons, and is frequently found alone, but still more 

 frequently in combination with the hexagonal prism, producing the 

 form seen in fg 7. It occurs frequently at Andreasberg, in the 

 Harz, and in the mines of Derbyshire. 



The rhombohedron fij. 3 is also of the second order, and is called 

 the first obtuser : its terminal edges correspond with the long diago- 

 nals of the faces of the ground-form, and therefore, with the same 

 breadth, its vertical axis is double that of the other : the inclination 

 of the faces at the terminal edges is 78 51'. In combination with the 

 ground-form, if the faces / predominate the form P appears as trun- 

 cations of the terminal edges ; if P predominates, the faces of / 

 produce truncations of the six lateral angles, the edges of intersection 

 being parallel to the inclined,, diagonals of P for two faces, and with 

 the horizontal one for the third. 



The rhombohedron fig. 4 bears to fig. 3 the same relation as this 

 does to the ground-form, the terminal edges of the first corresponding 

 with the inclined diagonal of the second : the inclination of the planes 

 to each other in the terminal edges is 65 SO'. 



Fig. 5 is one of the most common scalinohedrons, and is commonly 

 known as the Dog's-Tooth Calcspar, and is found frequently in Derby- 

 shire and other localities. It beara a close connection with the 

 rhombohedrons P and m, having the lateral edges of the first and 

 terminal edges of the latter, so that in combination with the first the 

 form fy. 8 is produced, and with the second it forms a bevelment 

 of the terminal edges : the inclinations of the faces in the terminal 

 edges are respectively 104 38' and 144 24'. This form frequently 

 occurs as twins, formed by two crystals growing on each other, their 

 principal or vertical axes being in the same right line, and the two 

 crystals so situated that the obtuser terminal edges of the one abut 

 on those of the other, and the acuter on the acuter. 



This mineral may be recognised by its perfect cleavage parallel to 

 the faces P : the specific gravity of the purest crystals is 2721 ; and 

 the hardness is in the scale of Mobs 3, being situated between gyps 

 and fluor-spar. It is of itself colourless, but frequently occurs of 

 various tints of yellow, green, red, brown, and even black, from the 

 admixture of impurities. Its glance is vitreous, with the exception 

 of the terminal face o, which generally presents a mother-of-pearl 

 lustre. It is usually more or less translucent, and when transparent 

 produces in a remarkable degree the double refraction of light : this 

 property is best seen in the varieties obtained from Iceland, and 

 hence known as Iceland-Spar, and occurs as the ground-form, being 

 in fact merely broken fragments of other larger crystals. 



The following are the names of the more common varieties of Cal- 

 careous Spar : Iceland Spar, Satin Spar, Chalk, Rock Milk, Calcar, -on* 

 Tufa, Stalactites, Stalagmite, Limestone, Oolite, Pisolite, Argentine, 

 Fontainbleau Limestone, White and Clouded Marbles, Statuary Marble, 

 Compact Limestone, Stinkstone, Anthracouite, Plumbo-Calcite, Mine- 

 ral Agaric, &c. 



CALCKDONY. [AGATE.] 



''A'LCEOLA, an extinct genus of Brachiopoda, which occurs in 

 the Palicozoic Strata, and especially in the middle group. Calceola 

 iccunt in this position in the Eifel, and in South Devon. 



CALCEOLA'KIA, a genus of very ornamental herbaceous or 



shrubby plants, belonging to the natural order Scrophulariacea;. Its 

 distinctive characters are principally, the flowers being diandrous, 

 with a two-lipped corolla, the lower lip of which is much larger than 

 the upper, and inflated so as to resemble a bag. All the species are 

 South American, and are confined either to the western side of the 

 Cordilleras, or to the southern extremity of the continent and its 

 adjacent islands : in Chili and the mountainous parts of Peru they 

 are so common as to give a peculiar appearance to the vegetation. 

 Some of them are lowlanders ; others inhabit the highest parts of the 

 Andes in the districts just below the regions of lichens and mosses ; 

 and thus, if both their wide geographical distribution and the various 

 elevations at which they occur are taken into account, they are exposed 

 to every kind of climate between those of England and Barbary. 



The greater part of the genus has yellow flowers, a few have purple 

 ones, and here and there in nature species occur with the two colours 

 intermixed, by the addition of spots of purple to the yellow ground- 

 colour, the latter changing the former to a deep rich brown. By 

 intermixing artificially the two colours natural to the genus a pro- 

 duction of hybrid varieties has resulted, and some crosses of extra- 

 ordinary beauty have been obtained, especially from C. integrifolia, 

 corymbosa, araclmoidea, Chiloensis, crenatiflora, viscosissima, &c, 



CALCITE. [CALCAREOUS SPAR.] 



CALEDONITE. [LEAD.] 



CALENDULA. [ALAUDA.] 



CALE'NDULA, a genus of plants belonging to the natural order 

 Composite, the -sub-order Corymbiferce, the tribe Cynm-ece, the sub- 

 tribe CalendulaceiE, the division Calendulea?. It has an involucre of 

 two rows with equal scales ; the flowers of the ray ligulate, pistil- 

 liferous, fertile ; the style divided at top into two stigmata ; the 

 flowers of the disk hermaphrodite, barren, the style undivided ; the 

 achenia unequal, curved, toothed, or muricated. 



C. an-tnfis, Field-Marigold, has the achenia cymbiform, muricated, 

 incurved, the outer ones lanceolate, subulate, muricated on the back. 

 This plant is common on the continent of Europe, and is found in 

 immense numbers in same of the vineyards of the Rhine. 



C. officinalis, Common Marigold, has cymbiform achenia, all of them 

 incurved, and muricated. Thia is the Souci du Jardin of the French, 

 Gold-Blume of the Germans, and Furrancio of the Italians. Although 

 common enough now in the gardens of Great Britain, and frequently 

 found wild, it is not a native of these islands, and has been introduced 

 from the south of Europe. This plant is a great favourite ingardei.s, 

 and continues to blossom till the approach of winter. It is often 

 grown in churchyards in this country, and in cemeteries on the 

 Continent, but this practice does not appear to be connected with any 

 superstition. There are several varieties of this plant found in gardens, 

 as the orange-coloured, the lemon-coloured, and the double. It 

 had formerly numerous virtues attribute 1 to it, but independent of 

 the bitterness of the tribe to which it belongs, and a rather morj 

 powerful volatile oil than is found in other species of the order, it 

 possesses no active properties. The flowers are used in some parts of 

 the country to give a yellow colour to cheese. In the Clock of Flora 

 of Linnaeus, it is said to open its flowers at nine in the morning and 

 to close them at three in the afternoon. C. plurialin has been named 

 from its flowers closing at the approach of rain. The petals of these 

 plants are sometimes employed to adulterate saffron. 



(Ljoudon, Encyclopedia of Plants ; Koch, Flora Germanica.) 



CALIDRIS, a genus of Birds belonging to the order Grallatorcs and 

 the family Charadriidce. It has the following characters : Beak as 

 long as the head, straight, slender, flexible, compressed at the base, 

 with the point dilated and smooth ; nostrils basal, lateral, narrow, 

 longitudinally cleft in the basal furrow, which extends to the smooth 

 point of the beak ; wings of moderate length, pointed, the first quill- 

 feather the longest ; legs of mean length, naked above the tarsal 

 joint ; feet with three toes, all directed forwards, with a very small 

 connecting membrane at their base. Gould, in his ' Birds of Europe,' 

 regards the Knot (Trinya canutua) as a species of Calidris. With this 

 exception the only British bird which is a species of this genus is 

 C. arenaria, the Sanderling. It is an inhabitant of most of the shores 

 of Great Britain and Ireland. It obtains its food by probing the 

 moist sands of the sea-shores, from which it obtains minute Mollusca, 

 shrimps, annelides, &c. It visits the shores of Sweden, and is stated 

 to breed still farther north. Sir John Richardson says it breeds on 

 the coasts of Hudson's Bay. It does not appear to breed in the British 

 Islands. (Yarrell, Britiih Birds.} 



CALI'GUS, a genus of Entomostracous Crustacea, separated by 

 Miiller, in which Latreille and Lamarck include the genus Pandarus 

 of Leach, but which Desinarest places under the fourth sub-division 

 or race of Pascilopoda : namely, tlio.su whii-h have fourteen feet, c.f 

 which the six anterior are unguiculated, the fifth pair being bifid with 

 the last joints fringed with fine hairs in the form of cilia. 



It has the body depressed, having its anterior portion covered by a 

 membranous shell in the form of a shield, narrowed posteriorly. 

 Abdomen narrower, of an elongated oval or nearly square shape, and 

 terminated by two elongated antennoc-like processes, cylindrical and 

 simple. There are two small conical antenna; situated on the anterior 

 border of the head, and directed laterally, and at the internal base of 

 these are placed the two distant eyes. Beneath the head there i an 

 obtuse beak. 



