MAM 



[ 157] 



MAR 



lacustrine formation, at North Cliff, in 

 Yorkshire, in which all the land and 

 fresh-water shells can be identified with 

 species now existing in that county. It 

 is supposed, from the prodigious number 

 of bones found in certain places, that the 

 mammoth must have existed in herds of 

 hundreds, or even thousands. According 

 to Pallas, there is scarcely a river, from 

 the Don, or the Tanais, to the extremity 

 of the promontory Tchuskoinosa, in the 

 banks of which the bones of the mam- 

 moth are not most abundant. There are 

 two large islands near the mouth of the 

 river Indigerska, which are said to be 

 entirely composed of bones of the mam- 

 moth, intermixed with ice and sand. 



The grinders of the mammoth are 

 formed of two substances only ; an inter- 

 nal bony substance, and a thick covering 

 of enamel. The form of their crown is 

 generally rectangular, the crown being 

 divided by spreading grooves into a cer- 

 tain number of transverse risings, each of 

 which is divided, in the contrary direc- 

 tion, into two large obtuse, and some- 

 what quadrangular and pyramidical points ; 

 the whole crown, when not worn, being 

 beset with large points, arranged in pairs. 

 In consequence of several of these teeth 

 being much worn down, not only to the 

 base of the pyramids, but even so low as 

 only to leave one square surface edged 

 with enamel, it has been concluded that 

 they were used in the trituration of ve- 

 getable food. M. Cuvier particularizes 

 three sorts of these grinders ; nearly 

 square, with three pairs of points, gene- 

 rally much worn ; rectangular, with eight 

 points, less worn ; and others with five 

 pairs of points, and a single smaller one, 

 scarcely the least worn. Cuvier consi- 

 dered he had distinguished five different 

 species. 



MANA'TUS. A genus of herbivorous ceta- 

 cea, placed by Cuvier in the family Ceta- 

 cea herbivora. The manatus appears to 

 have inhabited the seas of our latitude 

 during the Miocene and Pliocene periods. 

 The recent species are now found near the 

 coasts and mouths of rivers, in the torrid 

 zone. They have an oblong body, termi- 

 mated by an elongated oval fin : the 

 grinders have a square crown, marked 

 with two transverse elevations ; they are 

 eight in number throughout. Lamantin, 

 a name often given to manatus, is said to 

 be merely a corruption of Manatus. 



MA'NDIBLE. (mandibulum, Lat. a jaw.) 

 In insects, the upper jaws are called 

 mandibles ; the under jaws, maxillse. The 

 mandibles of insects are two strong, cor- 

 neous, somewhat bent hooks, their inner 

 margin being more or less dentate ; they 

 articulate with the cheeks at their broad 



basis, move by ginglymus, and are opposed 

 to each other like the blades of scissors. 



MANDI'BULAR. Pertaining to the jaw. 



MANGANE'SE. (manganese, Fr. maganese, 

 It.) A metal but little known in its pure 

 or metallic state, to which it is reduced 

 with much difficulty, in consequence of 

 its great affinity for oxygen. When pure, 

 it has a grayish -white colour, with some 

 lustre. Its texture is granular ; hardness, 

 nearly that of iron. Specific gravity 

 from 7-0 to 8'0. It has little or no 

 malleability. It absorbs oxygen by ex- 

 posure to the atmosphere ; and its melt- 

 ing point is about 160 W. 



In its metallic state, manganese is not 

 applied to any use. It is obtainable in 

 small quantities from the black oxide by 

 heating it in an intense furnace, with char- 

 coal and a little oil. 



The common ore of manganese is the 

 black, or peroxide, a valuable substance 

 to chemists, as that from which oxygen is 

 most easily obtained. When added in 

 small quantities to glass, it removes the 

 greenish or yellowish tinge which arises 

 from iron or other impurities ; but if 

 added in considerable quantity, it com- 

 municates to glass or enamel a violet or 

 purple colour. The ores of manganese 

 present much diversity in their exter- 

 nal characters. All minerals containing 

 any considerable quantity of this metal, 

 when melted with borax and a little nitre, 

 yield a violet glass. One of the ores of 

 manganese, known by the name of Black 

 Waddj is remarkable for its spontaneous 

 inflammation when mixed with oil ; the 

 reason of this does not appear to be un- 

 derstood. 



Oxids of manganese occurs principally, 

 though not exclusively, in primary and 

 transition rocks, in nodules or irregular 

 masses, in veins, and in beds. 



Of all the metals, the oxides of which 

 are neither alkalies nor earths, iron and 

 manganese are the most important, geolo- 

 gically considered. It is remarkable that 

 manganese is almost, though not quite, 

 as widely disseminated through rocks as 

 is iron, the proportions, however, being 

 much smaller. There is scarcely a rock 

 without iron, and there are very few which 

 do not afford some trace of manganese : ex- 

 cept, however, in the places where its 

 ores are worked, the latter exists only in 

 minute quantities. Its calculated amount 

 is greatest in mica slate with garnets, 

 where, as an oxide, it forms 1*23 per cent, 

 of the constituent parts of the rocks. 

 De La Beche. Cleaveland. Ure. 



MANGANE'SIAN. Containing manganese ; 

 resembling manganese ; having the pro- 

 perties of manganese. 



MA'RBLE. (marbre, Fr. marmo, It. mar- 



