9 8 



HARDWICKE'S SCIENCE -GOSSIP. 



present ; but the knowledge we have of the old sea 

 bottoms is partial, so that it sometimes happens that 

 while the known strata representing one great period 

 indicate the prevalence of one set of conditions, those 

 representing the succeeding one indicate the preva- 

 lence of a widely different set. The difference in 

 these faunas is frequently considered to be that of the 

 entire fauna of the two periods, whereas it may really 

 be that of the faunas belonging to different conditions 

 of the ocean of different periods, not the faunas 

 belonging to the similar conditions of those seas. 

 For instance, we know that the fauna of the deepest 

 parts of the Atlantic Ocean of the present period is 

 markedly different from that of its shores ; but pro- 

 bably if those species had represented a past period 

 in geology they would have been assigned to different 

 ages, if there were no stratigraphical evidence to 

 prove their contemporaneity. The distribution of a 

 species in time is also assumed to be continuous, so 

 that when it dies out it never recurs again, but its 

 place is often taken by a representative species. 

 Those species which can endure under many condi- 

 tions generally have an extensive range both in space 

 and in time, and are by themselves of comparatively 

 little use in synchronizing marine strata. Zones and 

 horizons are best marked by the maximum develop- 

 ment of one or a few species in association with the 

 same fauna. Such zones are generally of local 

 importance, and do not apply to the whole ocean of 

 the period ; and the synchronizing the fauna of 

 different areas is the most important work which the 

 student of the ocean has. yet to perform. The sea is 

 a barrier to the dispersion of many land animals and 

 plants ; and hence facts as to the distribution of 

 these afford a clue as to the position and persistence 

 of oceanic basins. The geological provinces of the 

 land are usually separated by wide and deep oceans. 

 Marine and non-marine forms are sometimes 

 mingled in the same stratum. This may be naturally 

 effected in many ways. In deep inlets of the sea, 

 into which rivers discharge themselves, it frequently 

 happens that the surface water is fresh enough for 

 the existence of fresh- water species, while the deeper 

 water is tenanted solely by marine forms. When 

 the individuals die, the fresh-water and marine forms 

 are mingled in the same deposit, and marine fishes 

 may have the remains of fresh-water species in their 

 stomachs. Land shells are sometimes blown on to 

 the shore between tide-marks, and may thus be asso- 

 ciated as fossils with the littoral marine fauna. The 

 sea-water flows up estuaries below the river water 

 for long distances ; and in many cases the alluvial 

 deposits about the mouths of large rivers are largely 

 composed of marine microscopical organic remains. 

 On the other hand, similar remains of terrestrial 

 forms of life are deposited on the sea bottom as a 

 consequence of dust-storms and dust-deposit gene- 

 rally on the surface of the sea. In many places 

 springs of fresh water well up on the sea bottom both 



near to and far from the shores ; and as these persist 

 for lengthened periods, it is not impossible that they 

 may be the means of distributing fresh-water remains 

 over a marine area. However, there appears to be 

 no case on record of any species of organisms having 

 been found having such areas for their special 

 habitat ; but this may arise from no one having 

 undertaken any search for the express purpose of 

 obtaining such forms, should they exist. As occur- 

 rences of this kind (excluding the surmise relative to 

 submarine springs) are known to happen now, we 

 should not overlook the possibility of their having 

 occurred in past periods. 



The contour and age of old seas may then be in- 

 ferred from three kinds of evidence: (i) Lithological, 

 or the superposition, nature and origin of sediments ; 



(2) Physico-geographical, or phenomena relating to 

 elevation and subsidence of the earth's surface, vol- 

 canic eruptions, position of land, denudation, and 

 others which need not be specially mentioned ; and 



(3) Biological. The inferred age of any particular 

 sea-bed ought to be based on facts belonging to all 

 three kinds of evidence, and an adequate knowledge 

 of old sea-beds is not attained until we have ac- 

 quired evidence as to the fauna of the various zones 

 and provinces of each period. Our knowledge of 

 the seas of past periods is but fragmentary ; but by 

 attending to the considerations suggested, we shall be 

 enabled to see more clearly where the deficiencies are. 

 Facts as to deficiencies or breaks, whether strati- 

 graphical or biological, are of great importance ; 

 such breaks are generally associated with lapse of 

 time, because changes require time for their develop- 

 ment ; and generally the greater the change the 

 longer is the time necessary to develop it. But such 

 changes are primarily associated with change of con- 

 ditions, and different conditions may abruptly suc- 

 ceed each other ; while similar conditions may recur 

 on the same area after a long interval of time without 

 any intervening strata. Hence stratigraphical breaks 

 do not always coincide with nor are proportional to 

 biological breaks. The cause of such breaks is a 

 matter for inquiry in each particular case, and it is 

 only from data thus acquired that one can judge of 

 the probable lapse of time indicated. 



PRIMITIVE MAN : 

 HIS TIMES AND HIS COMPANIONS. 



By the Rev. J. Magens Mello, M.A., F.G.S. 

 No. II. 



AS man advanced in civilization, or, as amongst 

 ruder tribes more cultivated ones made their 

 appearance, the forms of his implements became 

 more and more perfect, and better adapted to their 

 purposes. Bone would be at the same time more fre- 

 quently used ; and we have proofs that this was the 

 case in the fact that in the floors of some of our 

 caves, notably in those of Creswell and in the French 



