L I M 



[147] 



L I N 



trify in burning. All limestones effervesce 

 when a drop of strong acid is applied on 

 the surface ; and they dissolve entirely 

 in nitric or muriatic acid. The specific 

 gravity, hardness, and effervescence with 

 acids, taken collectively, distinguish lime- 

 stone from all other minerals." 



Limestone is found in the three great 

 classes of rocks, primary, transition, and 

 secondary ; but most abundantly in the 

 last. It is also not uncommon in alluvial 

 deposites, and is known by the name of 

 calcareous tufa. 



Mr. Macculloch has attempted to re- 

 vive the theory of some of the earlier 

 geologists, that all limestones have ori- 

 ginated in organized substances. He 

 says, "if we examine the quantity of 

 limestone in the primary strata, it will be 

 found to bear a much smaller proportion 

 to the siliceous and argillaceous rocks 

 than in the secondary ; and this may 

 have some connexion with the rarity of 

 testaceous animals in the ancient ocean." 

 He further infers, that, in consequence of 

 the operations of animals, the quantity of 

 calcareous earth deposited in the form of 

 mud or stone is always increasing ; and 

 that, as the secondary series far exceeds 

 the primary in this respect, so a third 

 series may hereafter arise from the depths 

 of the sea, which may exceed the last in 

 the proportion of its calcareous strata. 

 To this Mr. Lyell observes, if these 

 propositions went no farther than to sug- 

 gest that every particle of lime that now 

 enters into the crust of the globe may 

 possibly in its turn have been subservient 

 to the purposes of life, by entering into 

 the composition of organized bodies, I 

 should not deem the speculation impro- 

 bable ; but when it is hinted that lime 

 may be an animal product combined by 

 the powers of vitality from some simple 

 elements, I can discover no sufficient 

 grounds for such an hypothesis, and many 

 facts which militate against it. 



Primary limestone has always a granu- 

 lar structure ; but the size of the grains is 

 variable, and seems, in some degree, to 

 correspond with the relative age of the 

 mineral. Thus the limestone, which oc- 

 curs in beds in gneiss, and which is 

 supposed to belong to the older forma- 

 tions, has usually a coarse texture, and 

 large granular concretions. But when 

 its beds exist in mica slate, or argillite, 

 its texture, becomes more finely grained, 

 and its colour less uniform. Transition 

 limestone has a texture more or less 

 compact ; its colours are much varie- 

 gated ; and it often contains petrifac- 

 tions. Secondary limestone has a com- 

 pact texture, a dull fracture, and usually 

 contains shells, and sometimes other or- 



ganic remains. It is always stratified ; 

 but the strata are sometimes inclined, 

 sometimes horizontal. 



Mr. De La Beche states the quantity 

 of lime in granite composed of two-fifths 

 quartz, two-fifths felspar, and one-fifth 

 mica, to be 0'37 ; and in greenstone, 

 composed of equal parts of felspar and 

 hornblende, to be 7'29. 



LIMN^E'A. } (from Xijw^df , Gr.) A genus of 



LIMNE'A. $ fresh-water univalves, placed 

 by Cuvier in the order Pulmonea, class 

 Gasteropoda ; and by Lamarck in the 

 family Limnacea. The Limnea is an 

 ovato-conical, or turretted univalve. Like 

 the bulinij it has an oblong spire, and 

 the aperture higher than it is wide ; but 

 it may be distinguished from the bulini 

 by the very oblique fold on the columella. 

 The Limnea has been found fossil in the 

 neighbourhood of Paris. The recent Lim- 

 nea inhabits our lakes and pools ; its 

 shell is of a light amber colour. 



LIM'NITE. A fossil limnea. 



LI'MOUS. (from limosus, Lat. slimy.) 

 Muddy ; slimy. 



LI'MPID. (limpidus, Lat. limpide, Fr. lim- 

 pido, It.) Clear; pure; transparent. 



LIMPI'PITY. (limpidite, Fr. limpidezza, 

 It.) Clearness; pureness ; brightness; 

 transparency. 



LI'MULUS. The Molucca crab. A genus 

 of crustaceans, or entomostracans, having 

 a distinct carapace, or buckler, with two 

 eyes in front of the shield. The limulus 

 appears to approximate towards the trilo- 

 bite, and Professor Buckland says, ' the 

 history of this genus is important, on 

 account of its relations both to the exist- 

 ing and extinct forms of crustaceans ; 

 it has been found fossil in the coal forma- 

 tions of Staffordshire and Derbyshire ; 

 and in the Jurassic limestone of Aich- 

 stadt, near Pappenheim ; a small fossil 

 species is found in the iron-stone nodules 

 of Coalbrook Dale. In the genus Limu- 

 lus there are but faint traces of antennae, 

 and the shield, which covers the anterior 

 portion of the body, is expanded entirely 

 over a series of small crustaceous legs. 

 Of the tail of the recent limulus, savages 

 form a point to their arrows ; and when 

 thus armed, they are much dreaded. The 

 eggs of the limulus are eaten by the Chi- 

 nese. 



LINE OF BEARING. See Line of Dip. 



LINE OF DIP. Strata almost always de- 

 cline, or dip down to some point of the 

 horizon, and, of course, rise towards the 

 opposite point. A line drawn through 

 these points is called the line of their 

 dip. If a book be raised in an inclined 

 position, with the back resting lengthwise 

 upon the table, the leaves may be sup- 

 posed to represent different strata, then a 



