25S 



NA TURE 



[July 



1 1, 



1 89: 



Mars, and Saturn, obtained at the Lick Observalor}-. To the 

 Unglish Illustrated, Mr. Grant Allen contributes another 

 "Moorland Idyll"; and the inhabitants of "The Monkey 

 House in the Zoo" are described and illustrated by Mr. F. 

 Miller. In the Htitiiaititarian, Mr. J. d. Kaupert has a [Keudo- 

 scientific article upon " Some Results of Moilern Psychical 

 Research " : and in Chambers' s Journal, there arc articles worth 

 reading on death from snake-bile in India, the Carstairs Electric 

 Light KaiUvay, and citric acid. Geographers will Ix; interested 

 in a paper on "England and France in the Nile Valley," con- 

 tributed by Captain F. D. I.ugard to the National. Here we 

 may also mention that the Geografhiial /ounial coMAins a valu- 

 able paper in which Dr. H. K. Mill descril>cs his bathymetrical 

 sur\ey of the English lakes. Gooil Il'ords has an illustrated 

 article upon the manufacture of coal-gas, but neither 5ir/AHt7- nor 

 the Sunday Mas^azine have articles calling for connnent in these 

 columns. 



THE RE LA TION OF BIO LOG Y TO GEO- 

 LOGICAL INVESTIGATION^ 



I. 



Thk Ch.vracter a.M) Origin of I'ossii. Ke.\i.\i.\s. 



T N prosecuting the study of the fossil remains of animals and 

 ])lants, the investigator may have cither one or the other of 

 its two leading oVijccts in view ; but each lieing so closely related 

 to the other, it is always essential that they should be pursued 

 with direct relation to each other. In the first case, the leading 

 object to be attained is the extension of our knowledge of the 

 animal and vegetable kingdoms far beyond that which may be 

 acquired by the study of living animals and plants : and in the 

 second ca,se, it is to apply that knowledge to the study of 

 .strtictural and systematic geology. The olyecl in the first case is 

 purely |>al;eontological ; in the second, it is not only to acquire 

 jKil.eontological knowledge, but to ap|)ly it to various branches 

 of geological investigation. 



There are seven different natural conditions in which fos.sil 

 remains are recognisable, three of which relate to substance, 

 three to form, and one to Ixjth. To those relating to substance 

 the terms |K-rminerali.sation, histometaljasis, and carlKinisation are 

 here applied ; to those relating l(j form, the terms moulds, 

 imprints, and casts ; and to the one relating to Ixjth form and 

 .substance, the term pseudimiorphism. 



The term |>emiineralisation applies to that condition of fossil 

 remains of animals which differs least from their original con- 

 dition as [arts of living animals ; such, for example, .is bones of 

 vertebrates, shells of molluscs, tests of crustaceans, \c. The 

 term hislomelaU-usis is applied to that condition of fossdisation in 

 which an entire exchange of the original substance for another 

 has occurretl in such a manner as to retain or reproduce the 

 minute and even the microscopic texture of the oriyinal. 

 I'seudonuirphism of fossils is so nearly like that of mmeral 

 crystals, that this term is equally applicable to both. It consi.sts 

 in the repLacement of the original suljslance of the fossil by a 

 crystallisable or crjstalliscd mineral, such, for example, ascalcite, 

 pyrite, (quartz in the form r)f chalcedony, \c. , the iiriginal form 

 of the fossil iK'ing |K-rfeclly retained. The term carbonisation is 

 applied in this connection only or mainly to such miLsscs of 

 vegetable remains as coal, lignite, and |x;at. Moulds are cavities 

 in sedimentary rocks which were originally occupied by fossils, 

 the laller having been subsequently removed by the |K'rcolation 

 • if water containing a solvent of the fossils but ntil of the rock. 

 Imprinis ilo nut differ malerially in characler from moulds, the 

 former lenn lieing usually applied to impressions left in the ri>ck 

 by thin sul>stanccs like leaves of plants, wings of insects, &c. , 

 nft<-r ih'ir removal by decom|x>sition. Sometimes, however, the 

 ' shells and other fossils have Ijeen reduced to the 

 f imprints by the extreme pressure to which the strata 

 ■' have Ijcen subjected. Casts arc countcrixirts of 

 en produced by ihe filling of moulds with a 

 hn. 111. 11 of the original fossil. These are Ihe 

 pnii' li frfssils occur, or by which they are 



'ep" 'nally finds sjiccimens which indicate 



certain l!jiiiIi1ii.ii> ih.a .nc not fully recognised in the foregoing 

 de<>cri|>lions. 



' By C harln A. While. (Alxlracl of a «cric« of eight Muys publiiihcd in 

 the kcf^'Ti of the t'nilc<] .Stalc% National .MuKum.) 



Sei^imentarv Formations, their Char.^cter and 



LlMIT.^TION. 



There has lieen much difference of custom among geologists 

 as regards the use of the term formation, some applying it to 

 the smallest assemblages of strata which ix>.ssess common 

 characteristics, while others designate by the .same term those 

 series of formations for which the word system has been generally 

 used. That is, some ajiply the lenn formation to local or 

 limited develoiiments of strata, while others ajiply it to such 

 systems as the Devonian, Carboniferous, Cretaceous, &c. Thi> 

 term has generally been confined to the .stratified rocks, but by 

 a few authors it has been applied to the eruptive, and also to the 

 great crystalline, rock m.i.sses. In this ]xiper, however, the use 

 of the term formation is not only ci>nfined to the stratified rock^. 

 but it is restricted to those assemblages of strata which have 

 common distinguishing characteristics, whether they have little 

 or great geographical extent, or whether they aggregate a few 

 feet or thousands of feet in thickness. That is, the use of the 

 term is confined to those assemblages of stratified rocks 

 of .sedimentary origin' to which many authors have applied the 

 term group, and others the term terrane. 



The foregoing remarks concerning the characterisation oi 

 formations have been made with s|)ecial reference to those whicli 

 are more or less fossiliferous. It sometimes happens, however, 

 that fossils do not exist, or are not discovered, in certain 

 formations which are evidently of sedimentary origin. This may 

 have been <lue in some cases to the uncongeniality. as a faunal 

 habitat, of the waters in which the formation was deposited, and 

 in others to their failure to receive any fossilisable remains ol 

 animals and plants from the land. In i)ther cases, iheabsence*'! 

 fossils may have been due to their destruction or obliteration. 

 The latter has probably been the case with many melaniorphic 

 rocks and with the great pre-Cambrian series of stratified rock^ 

 generally. In all these cases the ft)rmations, while ihey may 

 possess more or less distinct ]>hy.sical characteristics, lack the 

 chief characteristics of sedimentary formations, namely, the 

 biological. 



The occurrence of an unfossiliferous sedimentary fiirmation a> 

 a member of an otherwise fos.siIiferous .series is unusual, but in 

 such a case its definition and limit.ition would be efl'eclually 

 accom|ilished by the inulerlying and overlying formations. In 

 the case, however of a great unfossiliferous series of stratified 

 rocks like the pre-Cambrian it is neces.sary to adopt a method Im 

 their study and classification b.ased wholly upon physical dal:i, 

 after the fact that they are pre-Candirian has lieen detemiincl 

 from biological data. Such a method of cla.ssifying anil charac- 

 terising tho.se unfo.ssiliferoHs stratified rocks as they occur in 

 North America has been proposed by I'rof. K. I). Irving'- and 

 afterwards elaborated by others. This great series of rock>, 

 as it is develoiied in .\merica, h.as such distinguishing general 

 characteristics and such magnitude and geographical extent, that 

 some geologists have thought it worthy ol^ being as.sigiied lo a 

 six;cial division of study, liul liecause no certain tr.aces tif organic 

 forms have been discovered in them, they have, so f;\r as it is , 

 now known, only the indirect relation lo biological geology 

 that has just been referred to. .Still it is not improhalile that 

 those strata were once fo.ssiliferoiis, and that the great series 

 was once niiide up of formations similar to ihose which have 

 been alre.idy defined, but it does not necessarily follow 

 that the divisions which are now recognisable by physical 

 characteristics corresi«ind to thftse formations. It is priibable 

 thai Ihey more nearly corres|«md to systems or to the larger 

 divisions of .sy.steins .Ts they are recognised in the greal scale of 

 the fossiliferous rocks of the earth. 



The following conclusions concerning formations are deducihle 

 from a cimsiileralicm of ihe available facts : — 



While formalionsare physical objects and have only a ])hysical 

 exislence, Iheir proper characlerisalion is cliielly biological. 



They are characlerisjible mainly by the iiissil remains of 

 atpialic faunn.s. 



Neither their jihysical nor biological limits are sliarply defined 

 except as a result of accidental causes. 



Their geographical limilalions are indefinite except llio^e 

 which were occasioned by .shore lines. 



1 To avoid frequent repelilion, the terms scdimenlnry formation alKl 

 Rlratified formation arc iivrd inlcrcIianKcal)!)' wtien applied lo formation* a* 

 defmcd atiovc. The Icrms >edimcnlary rocks, stralllied rocks, and fosMU- 

 ferous rfH-ks are also used iiilcrchanKeably. lull willi a somewhat more general 

 meaninu llian is intended Iiy Ihe two former terms. 



- IrvniK. K. I>. : "Classilicationof the Karly Cambrian and Pre-Cambrinn 

 Formalions." (.Seventh Ann. kcp. I'.S. licol. Survey, pp. 371-399.) 



NO. 1 34 1, VOL. 52] 



