198 



THE POPULAR EDUCATOR. 



There ia no danger of explosion in the main thoroughfares of 

 Jhe mine, where the fresh air is in great preponderance, any more 

 than there is danger.from an ordinary escape of gas in a room ; 

 but in the distant workings, where the fire-damp and air arc 

 mixed in certain proportions, the presence of a naked flame will 

 determine the combustion of the gas. 



Hence the miners are imperatively required to use the Davy 

 J.amp, which is an ordinary oil lamp whose flame is entirely sur- 

 rounded by a cylinder of iron wire gauze. As the explosive 

 mixture permeates through the gauze and touches the flame it 

 ignites, but as soon as the flame comes in contact with the wire 

 it makes the gauze hot. The heat thus taken from the flame 

 causes it to bo extinguished, and the combustion of the gas out- 

 side the lamp is prevented. As the gas is composed of carbon 

 and hydrogen, the products of its combustion with oxygen must be 

 water and carbonic acid gas. The water condenses on the sides 

 v>f the mine, and the heavy carbonic acid gas forms the dreadful 

 $x>ke-damp. 'There is never scarcely a hope of escape in the 

 neighbourhood of an explosion, for even if the unfortunate miners 

 are left unscorched by the hot flame of the ignited gas, the 

 instant after all the oxygen, necessary for their life, is found 

 to be combined with the carbon, and the mine filled with choke- 

 damp. Generally the force of the explosion has destroyed the 

 doors by which the ventilating current is directed, so that the 

 deadening fumes are not carried off, and they extinguish every 

 light and life. When the ventilation is not impeded, volumes of 

 the choking gas are rolled into the other parts of the workings, 

 and many a miner, under its deadening influence, sleeps his last 

 long sleep. 



From the preceding remarks our readers may be enabled to 

 imagine something of the history of the coal which sheds its 

 ruddy, cheerful blaze over the comfortable room. What we have 

 said, however, but faintly illustrates the hard lives of the men 

 who bring to the surface the treasure which gives our country 

 its untold wealth. 



FOSSILS OF THE LOWER CARBONIFEROUS. 

 C. CHARACTERISTIC OF THE STRATA. 



Polyzoa. Ceriopora gracilis, c. ; Fenestella plebeia; Glaucome bipin- 

 nata. 



Braehiopoda. Athyris hispida, c., oblonga; Chouetes convoluta, c., 

 eordida ; Orthis interlineata, c. ; semicircularis, c. ; Spirifer pro- 

 tensus, c., lineatis, calcaratus, macrouotus ; Strophalosia caperata, 

 c. ; Strophomena analoga ; Producta laxispiua, prffilonga ; Rhyn- 

 conella pleurodon. 



Conchifera. Avicula Damnoniensis, c., exarata, c., subradiata, c. ; 

 Aviculopecten granosus, grauulosus, c., nexilis, c. ; Pterinea spi- 

 nosa, c. ; Cucullea angusta, c., depressa, c. ; Mytilus Damnoniensis, 

 C. ; Nucula latissima, c. 



Gasteropoda. Euomphalus serpens, c. ; Loxonema sinuosa, c. ; Natica 

 nexicosta, c. 



Pteropoda. Bellerophon subglobatus, c. ; Urii. 



Cephalopoda. Clymenia bisulcata, c., Ifflvigata, c., undulata, c., pluri- 

 septa, c. ; Goniatites biferus, c., vinctus, c. ; Nautilus megasipho, 

 c. ; Orthoceras Phillipsii, c., striatulum, c., cinctum, undulatum. 



JSchinodermata. Adelocrinus hystrix, c. ; Cyathocrinus distans, c., 

 ellipticus ; Taxocrinus macrodactylus. 



Crustacea. Phacops granulatus. 



CHARACTERISTIC FOSSILS OF THE CARBONIFEROUS LIMESTONE. 



Foraminifera. Nodosaria ; Texularia. 



Zotphyta. Amplexus nodulosus ; Anlopora gigas ; Cyathophylluni 



expansum, plicatum ; Favosites dentifera, incrustans ; Gorgonia 



ziczac ; Heterophylla ornata ; Lithostrotion striatum j Strombodes 



floriforme. 

 Polyzoa. Ceriopora distans; Fenestella irregularis; Orbiculites anti- 



quus ; Polypora fastuosa ; Retepora undata. 

 Braehiopoda. Athyris depressa j Chonetes coincides; Orthis; Penta- 



merus ; Producta aculeata, gigantea, etc. ; Rhynconella reniformis, 



etc. ; Spirifer acutus, etc. ; Terebratula hastata. 

 Conchifera. Avicula squamosa, etc. ; Aviculopecten, about 60 species ; 



Inoceramus auriculatus, etc. ; Pecten stellaris ; Pinna 1 flabelli- 



formis ; Posidonomya tuberculata, vetusta, etc. ; Corbula senilis ; 



Cucullsaa obtusa; Cypricardia rhombea, etc. Modiola, Mytilus, 



and Nucula have several species each. 

 Gasteropoda. Euomphalus pentangulatus, etc. ; Loxonema brevis, etc. ; 



Murchisonia elongata, etc. ; Nerita spirata ; Patella curvata ; 



Pleurotomaria conica, etc. ; Turbo semisulcatus, etc. 

 Pteropoda. Bellerophon spiralis, etc. ; Cornularia. 

 Cephalopoda. Actinoceras giganteum; Goniatites atratus, etc. ; Nautilus 



biangulatus, etc. ; Orthoceras angulare, etc. 

 JJchinodermata. Actinocrinus amphora, etc.; Cyathocrinus conicus, 



etc. ; Platycrinus elegans, etc. j Rhodocrinus costatus, etc. ; Taxo- 

 crinus Egertoni, etc. 



Annelida. Serpula ; Spirorbis globosus, etc. ; Vermilia minuta. 

 Crustacea. Cyclus radialis; Cypridina primseva; Limulus trilobitoides. 

 Fish. Asteroptychius Portlocki, etc. ; Cladodus acutus, etc. ; Coch- 



liodus magnus, etc. ; Holoptychius Hibberti, etc. ; Oncbus sulcatus, 



etc. ; Psammodus rugosus, etc 



CHARACTERISTIC FOSSILS OF THE COAL MEASURES. 

 Plants. Adiantites, Annularia, Asterophyllites, Calamites, Caulopteris, 



Chondrites, Cyclopteris, Hippurites, Lepidodendron, Lepidostrobus, 



Neuropteris, Pecopteris, Sigillaria, Stigmaria, "Walchia piniformis. 

 Conchifera. Avicnla obliqua, etc. ; Axinus sulcatus j Modiola pro- 



ducta ; Mytilus triangularis ; Nucula acuta. 

 Gasteropoda. Euomphalus, Littorina solida, Loxonema reticulata, 



Natica vetusta, Pleurotomaria usocona, Turbo appropinquans. 

 Pteropoda. Bellerophon navicula, etc. 

 Cephalopoda. Goniatites dorsalis, etc. ; Nautilus concavus : Othooeras 



annulare. 

 Crustacea. Cypris arcuata, etc. ; Eurypterus Scouleri ; Limulus ro- 



tundus. 



Insecta. Curcunomdes Prestuicii; Corydalis Brongniartii. 

 fish. Acanthodus sulcatus ; Ctenacanthus, Gyracanthus, Holoptychius 



falcatus, etc. ; Megalichthys falcatus ; Onchus subalatns ; Palsjo- 



niscus carinatus, etc. ; Pleuracanthus ; Pleurodus. 

 .Reptiles. Archeeosaurus minor j Apateon pedestris. 



LESSONS IN GREEK. XXXVIII. 



FOEMATION OF THE TENSES OF IMPURE VERBS. 

 IMPURE VERBS are those whose characteristic is a consonant. 

 They are divided into two classes, mute verbs and liquid verbs. 

 Impure verbs differ from pure verbs in two ways : first, they in 

 part form the second tenses (second aorist, second future, 

 second perfect), and they in part undergo certain changes in 

 the formation of their tenses ; namely, first, a strengthening 

 of the stem by consonants or by lengthening the vowel of the 

 stem, and secondly by a change of the vowel of the stem, 

 which may be termed conversion. 



MUTE VERBS. 



Mute verbs have for their characteristic one of the nine 

 mutes : 



ir, ft, <t> ; as, \6iro>, I see ; rpjjSw, I nib ; ypatpta, I write. 

 K, y, x 5 as > TA.Ko>, I knit ; ayu, I lead ; -reu^o*, I make ready. 

 r, 8, 6; as, avvrta, I finish ; ctSco, I sing ; iretOw, I persuade. 



Many of those suffer certain changes in the stem or root. 

 The stem of the verb, firstly, is strengthened. The charac- 

 teristic consonant is strengthened ; thus, rvir-u becomes TUIT-T-W 

 by the addition of r to the stem. In such verbs there are 

 two characteristics, and two kinds of stems, the pure and the 

 impure. Thus, in TUTT-T-CO the mute TT is the pure characteristic, 

 and TTT the impure characteristic ; and TWIT is the pure stem, 

 while rvirr is the impure stem. In some cases the fc sound is 

 converted into rr or ffff, as <pptrro> or Qpiffffu, I shudder, the 

 stem of which is the pure form <ppm ; or, in others, the t sound 

 is converted into as <ppafa, I publish, from the pure stem 

 (ppaS. These strengthened and impure stems remain in only 

 the present and imperfect : 



Present. Imperfect. Future. 



t-Tvir-r-ov, 

 t-<f>piffffov, 



rvir-ff-ta (rvfyu). 

 <pptK-cr-<i> 



The strengthening may be in the stem-vowel. When this 

 strengthening occurs 



a is changed into r;. 



In this kind of verbs there is a division into pure and impure 

 stems. The pura stem appears in the second aorist active, 

 middle, and passive, as well as in the second future passive ; 

 for example 



PURE STEM. 



Present. Future. Perfect. 



a becomes 17 (aor. 2 pass. e-roK-rji'), TTJKW, Tyl-a, TtTTj/ca. 



t ' I ( e-TpijS-Tji'), rplfiai, Tpty<a, rerpitpa. 



I ,, ti (aor. 2 act. e-XtTr-oj/), \enra, \eityu, \f\onra. 



v v (aor. 2 pass, t-fypvy-ijv), (ppiiyca, <J)pO|co. 



i5 ,, eu(aor. 2 act. e-ipvy-ov), (pfvyca, <>eufo/ucu, ire<pfvya. 



For every form of the verb which cannot be deduced from 

 the present, another form of the present is assumed; for ex- 



