AMMAN (A. 



AMMONITES. 



lit 



primary furm of the crystal, like that of quartz, is a slightly obtuse 

 rluuntkiid. but it u usually found in the secondary form of a 6-sided 

 pri*m, tnuinnU<d at one or both ends by a 6-mded pyramid ; some- 

 time*, though rarely, the prism u wanting, and the pyramids being 

 then united baoe to base, the secondary crystal U a dodecahedron with 

 triangular facet, 



The amethyst is principally distinguished from common quartz by 

 iti colour, which in occasionally of every Khade of violet, or rather 

 purplish-violet, and this in the perfect amethyst in pretty equal 

 throughout the crystal : very commonly the summit* only of the 

 ujnUl are amethystine, the lower part being nearly colourless, or 

 tinged with green. By long-continued heat the colour U destroyed 

 and the crystals become white and opalescent Sometimes the crystals 

 are aggregated or fasciculated ; in the Palatinate they are found lining 

 geodes of agate, and in Silesia capillary crystals occur mixed with 

 micaceous iron ore. 



The crystals of the amethyst vary from diaphanous to translucent, 

 and they exhibit various degrees of splendour, l>oth externally and 

 internally. The fracture is commonly conchoidal, and the fragments 

 are of indeterminate form. Like quartz, the amethyst is sufficiently 

 hard to give fire with steel and to scratch glass ; and has also been 

 found, like it, with cavities containing water; it in infusible by the 

 common blow-pipe. According to Rose, it consists of 



Silica 97-50 



Alumina "25 



Oxide of Iron and Manganese . . . '50 



98-25 



AMMAXIA (in honour of John Amman, a distinguished botanist), 

 a genus of plants belonging to the natural order Lythractas. The 

 species are aquatic plants, with smooth opposite entire leaves, 

 4-cornered stems, and small pink or red (lowers. They are natives of 

 both the New and Old Worlds, and very generally distributed. One 

 species, A. rtricatoria, has a strong peculiar smell, and the leaves ore 

 very acrid. They are used by the native doctors of India for the 

 purpose of raising blisters, which they do in the course of half 

 on hour. 



AMMODYTES, a genus of fishes belonging to the division of 

 AiMdal Malacopteryyii and family A nguillida. The body is very long 

 and the head lanceolate. On the back is a dorsal fin extending nearly 

 its whole length. The anal fin is also long ; and the caudal, which is 

 fork I'd, is separated from both the dorsal and anal. Two species 

 occur on the coasts of the British Islands, the Ammodyta tuliimnns 

 and the Ammodytt* lancta. The former is the larger, and is distin- 

 guished by the greater size of the head, and by the dorsal fin, which 

 commences in a line with the extremities of the pectorals, whilst in 

 the A. lancm it commences in a line with the middle of the pectorals. 

 The Sand-Eel, by which name the first species is popularly known, 

 attains a length of between 12 and 15 inches. When alive the back 

 is of a dark bluish-green, and the sides and belly bright silvery-white. 

 It frequents sandy shores in great numbers, but is capricious in its 

 visits, more so than its congener. At the ebbing of the tide it buries 

 itself with great dexterity and rapidity in the wet sands to the depth 

 of from 4 to 6 inches, whence it is extracted by means of various 

 instruments, such as peculiarly formed gripes and sickles with blunt 

 edges, made for the purpose. It is much esteemed by fishermen as a 

 bait, and is also sought after on many parts of the coast as an article ' 

 of food, being very delicate eating when fresh, and excellent when 

 dried in the sun and grilled. 



The Sand-Launce, A mmodyta lancea, is a smaller species, and usually ' 

 of a more brownish hue, with a tinge of red about the head. It is 

 more abundant than the Sand-Eel, and has always been distinguished 

 from it by the fishermen, though for a long time confounded with it 

 In naturalists. The distinctions between the two species were first 

 pointed out by M. Lesauvage of Caen. Both appear to be generally 

 distributed through Northern and Western Europe. In Scotland the 



Sand-Eel U known by the name of the Homer, and in the Isle of M.m 

 the two specie* are distinguished from each other as the Gray Gibbon 

 and Red Gibbon. 



( Yam-ll, Hri'iA Fitka, vol. ii. ; Parnell, FMtt of Ike Frith of I 

 \ M MI ' MTKS, a fossil genus of Cephalopodoiis M.,1 /, allied to 

 the recent genus Nautilus. The species are known by the old i 

 niunv L'urnn Ammma. These Cornua Ammonii, (Jurnet if Amman of 

 the French, were so called from a fancied resemblance to the horns 

 with which the head of Jupiter Ammon was sculptured. In tin- i-iirlii-r 

 times their origin was variously accounted for. Some thought tlu-m 

 j petrifactions of real rams' horns, taking the name above-men t 

 in a strict and downright matter-of-fact sense ; others thought they 

 were the curled tails of certain animals ; some took them for petrified 

 marine worms rolled up ; others saw in them coiled serpents, 

 they were called Snake-Stones. The legends of the saints invested tin in 

 with a sacred interest. 



Of thousand mukr*, each one 

 Was changed into a coll of stone, 

 When holy Hilda pray'd. 



And the prayer, we ore told, was not only followed by petrifaction, Imt 

 by decapitation. We believe that there is a similar tradition 

 Keyna, who, when she found herself in a wood at Keynsham, bet\\ . < u 

 Bath and Bristol, surrounded by serpents, changed them by the fervour 

 of her devotions into headless stones. Nor wore these opinion- ion- 

 fined to the mere vulgar. Wormius dencrilx-d Ammonites as pctrilied 

 adders. I ,angius considered them to be either the vertebr.i 

 or convoluted marine insects. These notions were not lost on the 

 dealers; and there are few fossil collections which do not rvrn now 

 possess what was called ' a perfect Coi-nu Ammonit,' that is, an Ammo- 

 nite with a carved serpent's head ingeniously fitted on to the fo^-il 

 shell by way of aperture. Our limits will not permit us to dwell on 

 this fabulous part of the history of Ammonites further than to observe 

 that other learned men, Torellus Sarayna, Fracastorius, and others, 

 considered them as luus Katnra, formed by the plastic power of the 

 earth. The ancients held them in high estimation as very sacred and 

 of the highest value to the dreamer. Thus I'liny (' Hist. Mund.,' 

 xxxvi. 10), " Hammonis cornu inter sacratissimas Ethiopia; gemmaa, 

 aureo colore, arietini conitu eftigiem reddens, promittitur pncdivina 

 somnia representare ;" and even to the present time the Indians are 

 said to ascribe extraordinary properties to them. 



To the zoologist Ammonites are objects of great interest, and to I he 

 geologist they are of the utmost consequence. " It is easy," says M r. 

 1'hillips, in his ' Guide to Geology' (8vo. 1884), " to see how imjiortant, 

 in questions concerning the relative antiquity of stratified nn-1. 

 knowledge of Ammonites, since whole sections of them are cli 

 of certain systems of rocks." (sec. 82.) Dr. Buokland (' Bridgewater 

 Treatise,' p. 333), thus comprehensively describes the range of tin -. 

 extinct cephalopodous mollusks : " The family of Ammonites extends 

 through the entire series of the fossiliferous formations, from the 

 transition strata to the chalk inclusive." 



According to Mr. Owen's system, the Ammonites form tin' fourth 

 genus of his second family (Ammonitidit) of his first order 

 branthiaia, of the class (Jejihalopoda. In the opinion of all natu- 

 ralists this great group of fossils requires to be subdiviil.il. T!ie 

 Gonialitt* [GONIATITKS] of the Paltcozoic rocks have been effectually 

 separated; the Ceratitct of the triassic strata may be also withdrawn, 

 but still the number of genuine Ammonites which remain is too 

 enormous to be treated except in sections more or less founded mi 

 structural affinities. Without discussing what may l>c tl< 

 principles for such a classification, we may refer to that of Yon I'.neh, 

 as most generally accepted by geologists. This is mainly founded on 

 a consideration of the sutures, or sinuous lines at the surface of the 

 shell, formed by the edges of the diaphragmal plates which separate 

 the chambers. 



To illustrate this view of the subject we subjoin a few example .f 

 charncteriKtic Amnioiiitic sutures. 



Ammnnitn iiMarit (Powrrby). From Kellnway rock. 



Ammci.iln Walnttii (Sowwbr). From the Llan. 



Ammotiitn rrnuitm (Phillipo). From Spwton Clay. 



