386 



THE POPULAE EDUCATOE, 



A compact rock has its particles in close and firm proximity, but 

 one which is friable permits of being crumbled. A porous speci- 

 men is full of holes, like pumice-stone, but when the pores are 

 small it is said to be cellular or vesicular. Rocks are hard or 

 soft, but beyond a general application these terms are not much 

 in vogue. In mineralogy we shall find that much stress is laid 

 on the comparative hardness of minerals. 



Hocks which are composed of water-worn pebbles cemented 

 together are conglomerates. If angular fragments take the 

 place of the pebbles, a breccia is the result, which word is the 

 Italian for " fragment." A pebble is a small piece of mineral 

 matter, worn round by the action of water. When the sea-beach 

 is not sand, but stones rounded by the waves, the accumulation 

 of pebbles is a shingle. 



If the size of the pebble exceed a few pounds in weight, it 

 becomes a boulder. 



A stratum which has been deposited by aqueous agency is of 

 one of three characters. It is either of an arenaceous quality 

 that is, a sandstone ; or it is argillaceous that is, a clay ; or it 

 is a limestone. 



In each of the great systems in which rocks are classified, 

 these three species of rocks appear. Each system has its lime- 

 stone, its sandstone, and its argillaceous rocks, or its clay beds. 



Sand, of which arenaceous rocks are composed, is properly 

 small particles of quartz, which is the hardest constituent of 

 granite, and therefore most successfully resists the process of 

 attrition. 



Quartz is pure silex or flint, and may at once be recognised in 

 a specimen of granite, as those clear, semi-transparent grains. 

 When granite decomposes, these grains remain intact, or nearly 

 BO ; for silex is most difficult to dissolve. Particles of sand are 

 always rounded, as if by the action of running water. 



Sandstone is an aggregate of these particles, which are held 

 together in some cases without any apparent cement ; but often 

 calcareous or siliceous matter is present in a small quantity, 

 which binds the arenaceous particles together. Sometimes clay 

 or the oxide of iron forms this cement, and to this latter sub- 

 stance the red colour which frequently tints sandstones is due. 

 Some fine-grained sandstones are found which contain minute 

 scales of shining matter ; this is mica, another constituent of 

 granite, and such rocks are termed micaceous sandstones. These 

 sandstones are found among the earlier formations. 



Grit is applied to sandstones whose grains are very coarse. 



Argillaceous Rocks. Any earth which is sufficiently plastic to 

 be kneaded by the hand is, in common language, a clay. Strictly 

 speaking, clay is composed of siliceous and aluminous particles. 

 Kaolin, or porcelain clay, is the finest of the clays. Its composi- 

 tion is given in this table, in which it is compared with other 

 specimens : 



All clays are formed by the very fine disintegrated particles 

 of water-worn rocks. Mud is matter also formed of such par- 

 ticles, but it contains a mixture of animal or vegetable matter, 

 or both. Shale is hardened clay, but if it be softened by water 

 it will exhibit the plastic properties of that body. All clays 

 when breathed upon emit a peculiar earthy smell. 



Calcareous Rocks. All rocks of this description may be at 

 once discovered by the application of a few drops of any acid. 

 Effervescence at once takes place, owing to the escape of carbonic 

 acid gas, which is always associated with lime, forming a car- 

 bonate of that base. 



There are many varieties of limestone. Chalk, as we have 

 said, is due to the incessant work of minute animalcules, which 

 separate the lime from the sea-water to form their calcareous 



coverings, mixed with the shells of larger inhabitants of the 

 ocean. 



Marble is also carbonate of lime which has been submitted to 

 the action of heat, and thereby rendered crystalline. 



Mountain limestone is so called because it appears in ranges or 

 hills. It is very compact and dark-coloured. The walls in many 

 parts of Ireland are built of this admirable material, which is 

 found in great quantity in that island. In Sweden there is an 

 instance where a vein of granite has passed through a mass of 

 mountain limestone. This it rendered like marble where it had 

 contact with it, and the white crystalline rock gradually shaded 

 away to its original dark condition. The colour of this stone is 

 considered to be due to carbon in a state of minute sub-division ; 

 but the quantity is so small as to evade detection by chemical 

 means. 



Oolite is a species of limestone which appears in little round 

 grains, like the roe of fish ; hence its name. Each of these 

 grains has a particle of sand for a nucleus, round which the 

 limestone seems to have congregated. 



When magnesia is present in a quantity as much as thirty- 

 five per cent., the rock is termed dolomite. 



When clay and sand are mixed in a considerable quantity with 

 lime, a loam is formed. When only a little sand is present, and 

 the mixture is of a more firm texture than a loam, it is denomi- 

 nated a marl. It is not a usual thing to find any limestone 

 pure ; they all contain an admixture of foreign matter. 



These are the general characteristics of the great divisions of 

 rocks. Those deposits which are peculiar to the various forma- 

 tions will be alluded to in their proper places. 



LESSONS IN GREEK. XXIL 



THE NUMERAL ADVEBBS 



DENOTE how many times a number is to be taken, as " six 

 times six make thirty-six." Here six times is a numeral adverb ; 

 thus, Sis signifies twice, rpis three times. The termination of the 

 numeral adverbs is in general -KIS (-aim, -ret/as), which is annexed 

 to a cardinal, as Tfcrcra.pa.Kis, e<xm, tKa.TovTa.Kis. 



THE NUMERAL ADVEBBS. 



18. oKTUKaiStKaKis. 



20. flKOffOKlS. 



30. rpiaKovraKis. 

 40. rfrrapaKovraKis or 

 [rfffffapaKovrams. 

 50. 

 60. 

 70. 

 80. 

 90. 



100. fKarovraKis. 

 200. Sia.Kocria.Kis. 

 300. TpiaKoffiaKis. 

 1000. 

 2000. 

 10,000. 

 20,000. 



1. 07TO{. 



2. 8s. 



3. rps. 



4. rtrpoKis. 



fi <> 



7 iirra.it 



8. OKraKis. 



9. ewea/CIS, fVVOKlS. 



10. SeicaKts. 



11. ecSfKUKis. 

 12. 



13. 



14. rtrraptffKaiSfKaKis or rtff- 

 [ffaptffKaibfKaKis. 



16. fKKaiStKaKis. 



17. eTTTOKOtStKOKtS. 



EECAPITULATORY EXERCISES FROM THE CLASSICS. 

 1. Avaxapffis Kpfirrov t\fytv, fva $i\ov tx elt> ToAAov aiop, 

 77 iroAAous /jiriSfvos afious. 2. 'Avvotv, 6 icptff&vrfpos, fK rijt 

 AJ/SUTJS eirepafff fj.fya\r)v Svvafj.iv eis 2iKf\tav, itf<av juupiaSas 



~2,ripas Iffropovffi fj,fxpi rpiaKOffiwv fav frwv, Kai rovs XaASajous 

 uTrep ra fKarov fry $LOVI> \oyos (fffri). 4. ApyavBwvios, & 

 Taprrjffffuav /3affi\fvs, irtvTijKovra KUI tKarov tr-r] &iwffai Keyfrai. 

 5. 'O Tl\artev ereAeuTTjcre rta wpwria rrjs 078077$ Kai e/caroo-TTjs 

 OAu/tTrioSos, /3ious eros tv irpos roil oySoijKOvra. 6. ATj^T/rptos 

 TJS fiirf rea Nepcoi/r ffv fj.fv airti\fis fpoi rov Gavarov, aoi Se 77 

 tyvffis. 7. 2x^- c '0'TiKos airopofv, ra )3i/3Aia avrov firiirpaffKf, KO 

 ypafycov irpos rov irarfpa f\tyf, ffvyxaipf TI/JLIV, irarep, 77877 yap 7)/uas 

 TO piP\ia rpftpfi. 8. Avaxapffis 6 SKU^TJS fpun/tOets faro nvos, 

 n fffri iro\f(t.iov avBpuirois ; avrot, f<pri, eavrois. 9. 2x^ atrT " cos 

 oiKiav ir<a\<av, \i6ov air' avrrjs eis Sfiy/J.a 7repie<epe. 10. KpiTTjs 

 <av, afi ravra irtpi r<av avrcav yiyvcaffKe, ovStv irpos X a P' v ' Jrol<av - 

 11. H'uxTS firi/j.f\ov TTJS fffavrou. 12. BouAot aptffKeiv iraffi. 13. 

 Iloin-aij' fj&Xiffra fffavrov aiff\vvov. 14. *P^(rTov airavriav 



