122 



THE POPULAR EDUCATOR. 



(foramen, a hole). The shells of these minute creatures form 

 the great bulk of our chalk rocks. To confirm this fact, and 

 make the organic origin of chalk beyond dispute, by deep-sea 

 dredging vast areas have been discovered in the Atlantic Ocean 

 where the ocean floor is covered with calcareous mud. The 

 microscope reveals that this mud is composed of living fora- 

 minifera, who are hourly engaged in secreting the lime from 

 the water and forming their shells. Here then we have the 

 chalk beds in course of construction ; and in after ages, if the 

 world should still exist in its present form, and the bottom of 

 the Atlantic become dry land, there will be a bed of chalk, 

 unmixed with sand or pebbles or any other debris, and without 

 fossils of terrestrial plants or animals ; but probably the dis- 

 covery of ashes thrown overboard by our steamers, and now 

 and then some article of ship-craft, will be a sore puzzle to 

 the geologists of that distant day, unless they have the benefit 

 of our experience. 



Flints are generally found arranged in layers, at a distance of 

 two or three feet from each other. In all probability they owe 

 their existence to a similar cause as the chalk in which they are 

 embedded. All the creatures working at the bottom of the 

 ocean do not secrete lime ; many of them are clad in siliceous 

 shells. We can well suppose that for some reason or other the 

 quantity of lime held in solution in the water decreased, and in 

 its place there was a superabundance of silica. This would 

 cause the lime-secreting foraminifera to die out, and the animals 

 requiring a siliceous shell would occupy the area under circum- 

 stances advantageous to their existence. 



The fact that very frequently at the centre of a flint nodule is 

 found a fossil, is accounted for by Mr. Dana, by supposing that 

 when the microscopic organisms decomposed, tho alkaline 

 water of the sea would be able to take up a little of their silica, 

 and the rest would then have an opportunity of aggregating 

 round any foreign body, thus forming a concretionary nodule. 

 There are, however, some facts connected with chalk flints 

 which yet wait for explanation. 



Among the fossils found in the chalk, every one who has 

 hunted in a lime-pit knows that tho Ecliinoderms are the most 

 numerous. The spines are cleared off, and the plated shell 

 remains. The Ananchytes is a genus peculiar to the cretacean 

 period (Fig. 128, a, I). Other prominent fossils are Scaphites 

 cequalis (Fig. 129), Turrilites costatus (Fig. 130), Rhynconclla 

 octoplicata (Fig. 131), Terelratula biplicata (Fig. 132), Lima 

 spinosa, (Fig. 133), Ostrea carinata (Fig. 134). 



FOSSILS OF THE WEALD. 



Plants. Chora Valdensis ; Endogeuites erosa ; Equisetites Lyellii ; 



Sphenopteris gracilis. 

 ConcTu/ero.. Corbula alata ; Cyrenaangulata, major ; Mytilus Lyellii ; 



Unio aduncus, compressus. 

 Gasteropoda. Actaeon Popii ; Bulla Mantelliana ; Cerithiuin car- 



bonarium ; Melanopsis attenuata ; Paludina elcmgata, fluviorum. 

 Crustacea. Cypridea tuberculata, spinigera ; Estheria elliptica. 

 Fish. Acredus Hirudo ; JEchmodus mastodouteus ; Asteracanthus 



granulosus ; Hybodus dubius, subcarinatus ; Pycnodus Mantelli. 

 Reptiles. Chelone Mantelli; Iguanodon Mantelli; Pterodactylus 



Cliftii. 



FOSSILS CHARACTERISTIC OF THE LOWER GREENSAND. 



Plants. Abietites Benstedi ; Zaniiostrobus Sussexiensis. 



Sponges. Corns coutortoplicata. 



Corals. Holocystis elegans, Siphodictyuui gracile. 



BracJiiopoda. Discina leevigata ; Lingula truncata ; Khynconella 

 depressa, elegaus ; Terebratula celtica, oblonga. 



Condufera. Avicula depressa; Gervillia anceps ; Lima lingua ; Ostrsea 

 retusa ; Astarte obovata ; Cardium imbricatorium ; Cypriua angu- 

 lata ; Corbula striatula ; Cucullaea costellata ; Cypricardia 

 vmdulata ; Cyprina augulata ; Lithodomus oblongus ; Modiola 

 sequalis; Mytilus cuneatus ; Nucula obtusa; Pholadomya gigantea 

 Trigoiiia caudata, ornata. 



Gasteropoda. ActsBon marginatus ; Cerithium attenuatutn ; Littorina 

 conica ; Natica leevigata ; Pleurotomaria gigautea ; Turbo 

 munit.us. 



Cephalopoda. Ammonites furcatus, Martini ; Anoyloceras gigas 

 grande ; Nautilus plicatus. 



Eclrinodermata. Cardiaster Beustedi. 



Fish. Strophodus sulcatus. 



FOSSILS CHARACTERISTIC OF THE GATJLT. 



Foraminifera. Cristellaria obsoleta ; Dentalina leguinen. 



Corals. Bathycyatlius Sowerbyi. 



Brachiopodu- Ebynconella sulcata; Terebratula obtusa. 



'onchifera. Inoceramus sulcatus ; Mytilus Galliennei ; Nucula orna. 



tissima ; Pholas constricta. 

 jos'eropoda. Actoeon affinis ; Cerithium trimonile ; Natica gaultina; 



Pleurotomaria Gibbsii ; Eostellaria elongata, cariuata. 

 'ephalopoda. Ammonites biplicatus, circularis, crenatus, etc.; Ancylo- 



ceras spiuigeruin ; Belemnites attenuatus ; Hamites compressus; 



Turrilites catenatus, etc. 

 JcJiinodennafa. Cardiaster bisulcatus; Hemiaster asterias. 



CHARACTERISTIC FOSSILS OF THE UPPER GREENSAND. 

 'lants. Chondrites fastigatus. 

 BracJiiopoda. Lingula subovalis ; Rhynconella Grasiana ; Terebratula 



ovata. 

 'onchifera. Avicula grypliteoides ; Gryphcea vesiculosa ; Lima ornata ; 



Pecten elongatus, asper ; Cyprina globosa ; Trigouia Archiaci. 

 'osteropoda. Natica gentii ; Pleurotomaria Rhodani. 

 IcTimodenuafa. Auanchytes lasvis ; Cardiaster fossarius ; Cidaris 



iusignis ; Echinus inflatus, granulosus. 



CHARACTERISTIC FOSSILS OF THE LOWER CHALK. 

 'oraminifera. Dentalina Lorneiana; Globigerina cretacea; Texularia 



trochus. 

 Ji-ac/iiopoda. Rhynconella Cuvieri ; Terebratella incerta; Terebratula 



albensis, rugulosa, etc. 

 lonchifera. Inoceramus latus, striatus; Limaaspera; Ostrea virgata; 



Area subacuta ; Pholadomya decussata. 

 : asteropoda. Actaeon elongatus; Avellana cassis; Natica Dupimii ; 



Turbo gemrnatus. 

 'ephalopoda. Ammonites cinctus, falcatns, navicularis ; Hamites 



simplex ; Nautilus elegans ; Scaphites roqualis ; Turrilites 



costatus. 

 .EcTiinodermata. Ananchytus planus; Cidaris dissimilis; Discoidea 



cylindrica ; Goniaster latus. 

 Jeptiles. Chelone Benstedi; Ichthyosaurus campylodon; Plesio- 



saurus constrictus ; Pterodactylus giganteus. 



CHARACTERISTIC FOSSILS OF THE UPPER CHALK. 

 Plants. Confervites fasciculata. 



Amarphozoa. Spongia ramosa ; Ventriculites alternans, flexuosus. 

 Polyzoa. Actinopora Brongniarti; Alecto ramea ; Eschara caiicellata j 



Plustra tessallata ; Tubulipora; Vincularia. 

 BracTiiopoda. Crania costata ; Ehynconella octoplicata ; Terebratula 



carnea. 

 Conchifera. Inoceramus annulatus ; Ostrea curvirostris, triangularis ; 



Pecten virgatus; Pinna decussata; Modiola quadrata; Teredo 



rotundus. 

 EcTnnodermata Cardiaster excentricus ; Cidaris vesiculosa ; Goniaster 



angustatus ; Marsupites Isevigatus ; Ophiura serrata : Oriaster 



bulbiferus. 



LESSONS IN SPANISH. XVII. 



THE ARTICLE. 



THE definite article is to be used before all common nouns 

 taken in a general sense, and in the whole extent of their 

 signification ; as 



El odio levauta rencillas, 

 La caridad es pacieute, 

 Los hombres son mortales. 



Hatred excites stnfe. 

 Charity is patient. 

 Men are mortal. 



If the noun be not taken in a general sense, the article is not 

 used; as 



Hace buen tiempo, It is good weather. 



Tiene envidia, He has envy. 



The definite article is used before proper names of countries, 

 states, and days of the week ; as 



La Francia es un hermoso pais, 

 Juan volvera el Martes, 



Trance is a leautiful country. 

 John will return on Tuesday. 



The definite article is to be used before numerals indicating 

 the day of the month or the hour of the day ; as 



El seis de Enero, 



A las tres de la tarde, 



Tlie sixth (six) of January, 



At three o'clock in(oj) the afternoon. 



The definite article is used before nouns indicating the rank, 

 office, profession, or titles of persons when they are spoken of 

 (but not when they are addressed) ; as 



El General Brown es valiente, 

 La Senora Tranor no es pru 

 dente, 



General Brown is brave. 

 Mrs. Tranor is not prudent. 



The definite article (and not the indefinite, as in English) is 

 used before nouns signifying a certain weight, measure, size, 

 quantity, or number, when preceded by the price, and to specify 

 time ; as 



