M C 



[ 298 ] 



M L 



Mitres are found both fossil and 

 recent. 



MO'CHA STONE. (from Mocha, in 

 Arabia.) The quartz agathearboris 

 of Hau'y; called also dendrite 

 agate. A variety of agate, con- 

 taining in its interior very beautiful 

 delineations of leafless shrubs, trees, 

 &c., of a brown or dark colour. 

 These dendritic appearances are 

 supposed to be produced by the 

 nitration of the oxides of iron 

 and manganese into the fissures of 

 the agate. Mocha stones resemble 

 those agates which are found on 

 the Sussex coast called dendracliates. 



MODI'OLA. (from modulus, Lat. a 

 little measure.) A genus of shells 

 belonging to the family Mytilacea. 

 A transverse inequilateral bivalve. 

 The modiola is a littoral shell, 

 moored to rocks, stones, and shells. 

 One species, modiola discors, floats 

 free, enveloped in its own silky 

 byssus. Fossil species have been 

 found in the neighbourhood of 

 Paris, and in this country. 



MO'LAB. (from mola, a mill, Lat. 

 molai/re, Fr.) A grinder- tooth. 

 The large double teeth are called 

 molar teeth, or grinders ; these are, 

 however, subdivided according to 

 their different forms ; thus, those 

 with two fangs are called bicuspid, 

 or false molar teeth. The posterior 

 molar teeth are differently shaped 

 in carnivorous animals, being raised 

 into sharp, and often serrated, 

 edges, having many of the proper- 

 ties of cutting teeth. In insecti- 

 vorous and frugivorous animals, 

 their surface presents prominent 

 tubercles, either pointed or round, 

 for pounding the food; while in 

 graminivorous quadrupeds they are 

 flat and rough, for the purpose 

 simply of grinding. 



MOLA'SSE. (from mollis, soft, Lat.) 

 The name given to a soft green 

 sandstone found in Switzerland ; 

 one of the most recent of the ter- 

 tiary deposites. In the Molasse of 



Switzerland there are many depo- 

 sites affording sometimes coal of 

 considerable purity. 



Until the place of the molasse in 

 the chronological series of tertiary 

 formations be more rigorously de- 

 termined, the application of this 

 provincial name to the tertiary 

 groups of other countries must be 

 very uncertain, and it will be desi- 

 rable to confine it to the tertiary 

 beds of Switzerland. Lycett. 



MO'LECULE. (moUcule, Fr. petite partie 

 d'un corps.) A minute particle of 

 a mass or body, differing from 

 atom, inasmuch as it is always a 

 portion of some aggregate. The 

 ingredients of granite, and of all 

 other kinds of crystalline rocks, 

 are composed of molecules which 

 are invisibly minute, and each of 

 these molecules is made up of still 

 smaller and more minute molecules, 

 every one of them combined in 

 fixed and definite proportions, and 

 affording, at all the successive 

 stages of their analysis, presump- 

 tive proof that they possess deter- 

 minate geometrical figures. 



MoLLifscA. (mottusca, a nut with a 

 soft shell, Lat.) According te the 

 arrangement of Cuvier, the second 

 great division of the animal king- 

 dom. This he subdivided into six 

 classes, namely, Cephalopoda, Pter- 

 opoda, Gasteropoda, Acephala, Bra- 

 chiopoda, and Cirrhopoda. A vast 

 multitude of species, possessing in 

 common many remarkable physio- 

 logical characters, are comprehended 

 in this great division. In all, as 

 their name imports, the body is of 

 soft consistence ; and it is enclosed, 

 more or less completely, in a mus- 

 cular envelope, called the mantle, 

 composed of a layer of contractile 

 fibres, which are interwoven with 

 the soft and elastic integument. 

 Openings are left in this mantle 

 for the admission of the external 

 fluid to the mouth and to the respi- 

 ratory organs, as well as for the 



