

61 



LE ;.<)<}. X. 



-ilLS. 



A. FOSSIL, as tho <l. rr. ,ni..:i .,:' ih.- \vunl indicates (fossns, dug 

 </>), means anything which is exhumed from tho earth. Tho 



I to Di-^iiaic reaiaiiiH, the nub- 



of which liiis imdorgoiiu uiineriilimitiou or petrifaction. 



i!uil material of tho body bo still unchanged, 



the term - ' -*il is nomotimcs used, though it is quito un- 



ntcannry ; tor if any organic body had only boon buried a few 



years, without impropriety it might be colled a fossil. 



Th.-re :ir.i three kimls of fossils : 



1. \Yhen tin- :uiii'i:ii or vegetable remain is embedded in clay, 

 or some P in ! p"-it,, and pro.sorvod in its natural state. 



-. \Vhcn tlit! original substance of the body has been removed, 

 unl p:iriicl.-< of mineral matter have replaced the organic par- 

 ticles, thus forming an exact model of the embedded body. 



A hen all tho hollow parts of tho nhell have become filled 

 with fino particles of iniul, thua forming a cast of the inside. 

 At a subsequent timo tho shell bocamo removed, and this cast 

 remained to per- 

 petuate the me- -^^~//?sx*.___ ^ fig. 18. 

 mory of tho 

 Iniricd animal. 



Fig. I6a is a 

 good example of 

 this action. The 

 "fossil screw" is 

 common in the 

 limestone of the 

 middle oolite 

 the coral -rag 

 and is nothing 

 but a cast of tho 

 internal struc- 

 ture of the pha- 

 'l<i (Fig. 

 166). Fig. 17 

 shows the cast of 

 the pleurotoma~ 

 s-ia (Fig. 176) in 

 situ. The lime 

 of which the shell 

 was composed 

 was, in each in- 

 ihmce, either 

 lissolved by the 

 water under 

 certain circum- 

 stances, or other- 

 wise destroyed. 



The space it occupied is evident in Fig. 17a. In this class are 

 placed the prints of tho footsteps of birds and beasts, which are 

 found on rocky slabs. In one sense they are the remains of 

 animal life. 



The Process of Fossilisaiion. The simplest form of fossilisa- 

 tion is when water charged with some mineral in solution satu- 

 rates a substance, and in its pores deposits the mineral matter. 



It is in this manner that petrifying springs " turn into stone " 

 porous bodies immersed in their waters. 



This mode of fossilisation may be practically illustrated by 

 steeping thin vertical slices of deal in a solution of green vitriol 

 sulphate of iron for several days. The wood is then removed 

 ind dried, and upon exposing it to a red heat the vegetable 

 matter is consumed, and nothing but oxide of iron remains, 

 which has so exactly taken the form of the deal that even tho 

 easts of the dotted vessels which characterise this species of wood 

 are visible under the microscope. 



In this case, as in all cases of recent petrifaction, the original 

 fibre of the wood is left intact, and the pores only are filled up 

 with the mineral matter held in solution in the water. But 

 after a lapse of time a further process sets in, and the original 

 matter of the body begins to decay. Particle after particle 

 makes its escape, either as gas, or, becoming loosened, drops out 

 of its place, and its position is at once filled by an atom of 

 mineral matter. Thus, in time, all the body is replaced by the 

 deposit in which it is buried, and a fossil produced which faith- 

 fully preserves the structure of the plant or shell. 



Pig. 22. 



Soft animal tiwoM can never be foHsilued, bat daring their 

 process of putrefaction the gases they emit cause various 

 chemicu . s to be thrown down from the water in -arhich 



they are immersed. 



'1'liD ntu'lcnt will frequently find a nodule of clay which, when 

 broken, is found to contain the fossil of an ammonite, or some 

 other shell-fiMh, bright with a metallic crust of iron pyrites. The 

 presence of this is easily accounted for by tho fact that albumen, 

 a constituent of all animal tissues, contains sulphur, and when 

 undergoing decomposition this sulphur escapes a* sulphuretted 

 hydrogen gas. If the water be impregnated with iron, a sulphide 

 cf that metal would be found at the place where the gas was pro- 

 duced, and thus the fossil would be built up partially of iron sul- 

 phide. Those replacements of matter frequently take place more 

 than once, and with such wonderful accuracy that a piece of wood, 

 whose ligneous matter had been replaced atom for atom by car- 

 bonate of limo, and this again by silica or flint processes which 

 may have taken ages for their completion still retains its 

 structure ; and, under the microscope, reveals sufficient of the 

 arrangement of tho woody fibre to determine its nature. 



Tho observant 

 reader will at 

 once perceive 

 that the best fos- 

 sils will be found 

 in rocks of tho 

 finest grain, such 

 as limestones, 

 whereas sand- 

 stones embed 

 fossils which re- 

 tain no delinea- 

 tion of delicate 

 structure. It fre- 

 quently happens, 

 especially with 

 fossils of car- 

 bonate of lime, 

 that a process 

 of crystallisation 

 has caused a re- 

 arrangement of 

 the particles, ut- 

 terly obliterating 

 all indication of 

 organic struc- 

 ture. 



This subject of 

 fossilisation is 

 not sufficiently 

 understood to 



warrant our dwelling further upon it. We have indicated the 

 general outlines of the process, but the more intricate questions 

 require a greater knowledge of chemistry than we can presume 

 our readers possess. We only would observe that it must 

 not be supposed that in all cases the lapse of many years was 

 required for the completion of the mineralisation, for it fre- 

 quently happens that the very soft tissues of plants, which would 

 rapidly decay, are beautifully fossilised, especially in siliceous 

 matter, indicating the occasional rapidity of the process. 



In enumerating the characteristic fossils of the various 

 systems of rocks, we shall so frequently have cause to refer to 

 the generic names, that we give a full classification of the animal 

 kingdom omitting the families as arranged by Professors 

 Ower and Huxley. We shall not have occasion to mention many 

 of the orders here given, but we judge it important to give a 

 table of reference, so that the relative position of those fossil* 

 we do not mention may be comprehended. The orders in italics 

 are only known in a fossil state. 



KINGDOM, AM M A I.I A. 

 SUB-KINGDOM, VEETEBBATA. 



Class I. MAMMALIA. 

 Sub-class. Placentalia. 



Arclu-]>Cf]>hal<i : Erampltt. 



Order 1. Bimana . . . Man. 



Gyrencepliala .- f Catarhini : Old World Monkeva 



2. Quadrumana . . ( Platyrhini : New ,, 



I^Strepsirhini: Lemurs. 



