sTi;.\ri<,i;.M'iiir.\i. PALEONTOLOGY 



17 



tin- .-tiv;un.- ilm-ing ll<>od>, ami \\viv luirii-d in the eatuarinc deposits 

 at the mouths of large rivers. 



Tin- civ.ttiitvs which inhabit tin; sea have a inm-h U-tt.-r chance 

 of being preserved as fossils, since deposits of one kind or another 

 are constantly being formed over large areas of the sea-bottom, 

 especially where subsidence is in progress. Yet even among marine 

 forms of life there are many which would only rarely be entombed ; 

 those animals, for instance, which live on rocky shores and in clear 

 water would not be preserved except where deposits of limestone 

 were in process of formation. The majority of the creatures 

 embedded would be those which lived on sandy and muddy 

 bottoms, together with some of the free-swimming forms which 

 moved through the water above. 



Lastly, of the creatures so embedded only a small proportion 

 would ultimately remain ; those, namely, which possessed hard 

 structures capable of fossilisation after the softer parts had decayed 

 and disappeared. The following table shows at a glance which 

 kinds of animals, out of all those which live in the sea, would be 

 likely to leave memorials behind them and which would perish 

 without leaving any trace of their existence. 



Sub-kinsdoiiis. 

 Protozoa. 



Porifera. 



Ccelenterata. 



Echinoderma. 

 Vermes. 

 Arthropoda. 

 Molluscoida. 



Mollusca. 

 Vertebrata. 



Groups with Hani Structures, 

 f Foraminifera. 

 \Radiolaria. 

 /Silicispongia?. 

 XCalcispougiae. 



Sertularida. 



Hydrocorallina. 



Graptolitoida. 



Stromatoporoidea. 



Madreporaria. 



Some Alcyonaria. 



All classes. 



fTubicola and the horny 

 \ jaws of Nereids. 



All classes. 

 /Bryozoa. 

 \ Brachioporla. 

 fLamellibranchia. 

 I Scaphopoda. 



| Gastropoda except 



{.Cephalopoda except 



/Teeth, bones, and 

 \ scales of all kinds. 



Perislimble Group*. 



FlagellaU. 



Infusoria. 



Myxospongue. 



Ceratospongue. 



Hydroida (except 

 Sertularida). 



Siphouophora. 



Disco phora. 



Actimaria. 



Alcyonaria (some). 



Ctenophora. 



NOM. 



/Hirudine*. 

 \01igoc hta. 



NudibranchiaU. 

 some Cuttle-fish. 



Tunirata. 



But although all the classes of creatures entered in the second 

 column possess hard parts which are capable of preservation, H 

 does not follow that these are always preserved. Their conversion 



C 



