November 1, 1887.] 





♦ KNOW^LEDGE ♦ 



JLLUSTRATED MAGAZINE^ 

 lENCEiITERATUllE,& AR^ 



LONDON: NOVEMBER 1, 1887. 



THE STREAM OF LIFE. 



OMONG the results of modern, nay, of quite 

 recent, scientific research, I know none 

 more impressive than the recognition of the 

 stream of life, animal and vegetable, which 

 has flowed over the earth during millions 

 of past years. Starting we know not how, 

 coming we know not whence, the stream of 

 life has left traces of its existence in all the rock strata of 

 the earth from the palseozoic onward through the secondary 

 and tertiary .systems, onward to the pleistocene and to those 

 strata which are called recent, though some of them, 

 measuring their duration as men measure time in consider- 

 ing the progress of i-aces and of nations, seem of vast 

 antiquity. 



Let us consider how the history runs, not entering into 

 details, but taking such a survey as shall bring the broad 

 features of the scene before us, and show its cosmical rather 

 than its merely terrestrial aspect. 



How first the earth's crust was formed we know not, for 

 the traces of the first formative processes have long since been 

 swept away. Probably each portion was formed again and 

 again, .solidifying and melting, and resolidifying and re- 

 melting, many times over before it finally assumed the 

 solid condition. In some cases the solid part of the crust, 

 being of greater specific gravity than the molten, would 

 sink as fast as formed, to melt again, and again return to 

 the surface, not finally solidifying in a permanent way until 

 many hundreds of thousands, perhaps million.s, of years 

 had passed. 



Whether any part of the present crust of the earth can 

 be regarded as representing the solid crust fashioned when 

 first these alternations were completed may well be doubted. 

 The so- called Archaean rocks have been supposed by some 

 to be the primeval crust of the planet. But others regard 

 them as belonging to a much later stage. And others yet 

 admit that we cannot tell what interval separated the 

 formation of these, the most ancient rocks of the present 

 earth, from the first formation of a ci'ust upon that region 

 of the eartii where the Archfean rocks are found? But 

 this, at any late, is certain : Whenever the Archaean 

 rocks, which have been exposed in various parts of the 

 earth by long continued processes of denudation, were 

 actually formed, they have mostly (if not all) undergone 

 great changes during the time that they have been buried 

 beneath strata formed later. Moreover, it must be remem- 

 bered that the lower primary rocks which were originally 

 deposited on these Archsean rocks were formed from them 

 by processes ot denudation, and that, therefore, we cannot 

 expect to find anywhere the ancient face of the first-formed 

 cru.st. Indeed, denudation in those remote times, certainly 

 20,000,000, and probably 100,100,000 years ago, was 'a 

 very much more active process than denudation as it takes 



place now. For the waters of the ocean were greater by 

 one-half in quantity, were intensely hot, were loaded with 

 destructive acids, were more actively moved ; while the 

 air was not the pure life-nourishing air we breathe now, 

 but an atmo.-^phere whose breath was fire, laden with 

 destructive vapours, swept by tremendous storms, and 

 beai-ing clouds fiom whose bosom descended torrents of hot 

 water, mixed with sulphuric acid, boracic acid, and other 

 powerfully acting liquids. By these destructive agencies 

 the first formed crust of the earth must have been rapidly 

 denuded, and fresh layers formed at the lower levels, to be 

 raised while the higher levels were dspi'essed, fresh denuda- 

 tion following, and fresh layers being formed, probably 

 during millions of years, before life was possible upon the 

 earth. 



It appears to me, indeed, that in the existence of fossil 

 traces of life, animal and vegetable, in the lowest of the 

 palseozoic rocks, we have decisive evidence that immense 

 periods of time must have separated the formation of the 

 rocks next below them from the first formation of the 

 earth's solid crust. For it is certain that during millions 

 of years following the .solidification of the earth's crust, life 

 must have been impossible. Even apart, therefore, from 

 the decision of the much-vexed question whether the forma- 

 tion named Eozoon found in the Archa?an limestones of 

 Canada is to be regarded as the fossil evidence of a reef- 

 building animal (a Foraminifer), which would throw back 

 still farther the time of the first .solidification of the crust, 

 we may safely conclude that the Archaean rocks represent 

 formations which had no existence with their present 

 structure until millions of years after the earth first had a 

 solid surface. 



With our present ideas respecting the laws of biological 

 evolution (ideas based, be it rememljered, on observed facts) 

 we may deduce the same conclusion from the character of 

 the fossils found in the lowest of the primary or palaeozoic 

 rocks. We know that whatever may have been the actual 

 beginnings of animal and vegetable life on the earth, the 

 flora and fauna even of the lowest palfeozoic strata cannot 

 have come into existence save as the product of immense 

 periods of past time. In the Lower Silurian rocks, indeed, 

 we have but few fossil traces of the vegetation of the 

 remote time when they were formed ; but this is chiefly 

 due to the fact that the Lower Silurian rocks are chiefly of 

 marine formation. But the animal life, even of the oldest 

 .stratified rocks, suffices to decide the question of duration 

 in the most emphatic manner. Of course, the record is 

 incomplete ; but in its very incompleteness it is the more 

 decisive. We find complex and advanced forms, while the 

 simpler forms, which necessarily existed at the same time, 

 have left no trace of their existence. We can under.stand, 

 then, how all forms of life, simple and complex, animal and 

 vegetable, belonging to earlier strata, have disappeared, 

 leaving no fossil evidence. And the positive evidence 

 given by the fossils we do find, while thus giving to the 

 negative evidence its true meaning, has its own definite 

 and unmistakable value. 



If we consider, for example, but a single class — say the 

 Trilobites (now extinct, though transiently represented in 

 the Ciirly life stages of the King Crab) — we have as decisive 

 evidence of enoi'mous preceding time-intervals as if we had 

 fossils of 10,000 species of Silurian life, animal and vege- 

 table. Those strange crustaceans existed at the remotest 

 time to which geological history looks back, in many 

 diflerent forms. Each had a strong head-shield to protect 

 its head, a smaller tail-shield, and a ringed body which 

 could be so curled that the two shields came together, and 

 the whole body was protected. Some were nearly two feet 

 in length (possibly some were much larger, but I speak 



