♦ KNOWTLKDGE ♦ 



[November 1, 1887. 



only of existent fossil evidence), and from this size they 

 ranged down to minute forms, such as the Agnosfus 

 Princi'ps, which was less than half an inch long. The 

 number of rings also varied, the Agiwstus having but two, 

 the ilicrodiscus four, the Eri»ni/.9 no fewer tlian twenty- 

 four. Still more strikiug evidence of development, re- 

 quiring hundreds of thousands of years for its full work, is 

 found in the complex ej-es of the more advanced species of 

 trilobites, for while the Ai/nostus was blind, most of the 

 trilobites had eyes, some with fourteen facets, others with 

 as man}' as 1.5,000 ! All thi-ough the Silurian period these 

 crustaceans continued to thrive and multiply and develop 

 into varied forms. But as the millions of years represented 

 by the palaeozoic strata passed on, evolution in the race of 

 trilobites resulted in the development of other races better 

 fitted for the changed conditions of life ; we find no traces 

 of any trilobites later than the carboniferous age; and in 

 that age we find only four, all of which were small. Doubt- 

 less many others existed of which no fossil traces have been 

 left. Doubtless, also, triloliites continued to much later 

 times than the fossil evidence attests. 



We cannot trace the series of crustacean i-aces which 

 connect the trilobites with their descendants in secondary, 

 tertiary, and recent ages. We cannot even tell what 

 creatures have descended from the trilobites, excepting here 

 and there a race or so, or along what line the descent 

 travelled. We know only that those races which retained 

 their triloliitic characteristics died out, those only survivinj. 

 ■which adapted themselves by changes of structure to sur- 

 rovinding conditions. 



But the Silurian rocks (the lowest and most ancient of all 

 rocks known to have been life-bearing) were not without 

 vegetable life, and the fossils telling us of the existence of 

 vegetable life show also that immense periods of life must 

 already have pissed before that life began. In the Upper 

 Silurian strata we recognise the spores and stems of flower- 

 less plants (cri/p/ogams). Club mosses and ferns were par- 

 ticularly conspicuous in the flora of those palfeozoic times. 

 "We can dimly picture the Silurian land," says Geikie, 

 " with its waving thickets of fern, above which lycopod 

 trees raised their fluted and starred stems, threw out their 

 scaly, moss-like bi'anches, and shed tlieir spiky cones." But 

 it is only because the cones and spore cases of the club 

 mosses and the tough tissues of the fei-ns have been well 

 fitted to withstand destructive agencies, and so have remained 

 in fossil form (some few even of these), that we are able to 

 speak of these as forming characteristic features of the old 

 Silurian thickets. Doubtless man}- other forms of vegetable 

 life existed, whose traces have long since entirely disappeared. 

 The wonder is, considering the immense remoteness of 

 Silurian time, that any trace whatsoever, either of animal or 

 vegetable life, should have reiched our time. 



^lost strange is it to think that even of the denizens of 

 those ancient thickets some traces have been found. Be 

 mains of scorpions were discovered in the Silurian locks of 

 Sweden, Scotland, and the United States almost simul- 

 taneously in 1884; while in those of France, also in 1884, 

 the remains of an ancient cockroach were found. Where 

 scorpions and cockroaches abounded, not only must there 

 have been many other forms of land animals, but animal life 

 must have exi.sted on land during hundreds of thousands of 

 years. For the laws of biological evolution do not permit 

 us to believe in the development of living creatures so com- 

 plicated in structure as the Arachmdcp and the Jllnffiihc, 

 save in vast periods of time. 



In these early stages of paljeozoic time we find evidence 

 not only of multitudinous life, but of many forms of life. 

 StUl within the Silurian era we find vertebrate forms in 

 fishes akin to the modern sharks, the sturgeon, and the gar- 



pike. (Tie catfish shares with the cockroach the honour of 

 descent from Silurian times.) Onward through Devonian 

 time vertebrate life presents itself still only among fishes, 

 but now in ever increasing variety and numbsrs. New 

 forms of crustaceans — the Eurypterids — having affinities 

 also with the Arachnids? (scorpions), began to replace the 

 trilobites, from which probably they had descended, though 

 after transformations requiring vast periods of time. 



Many other forms of life existed also throughout the 

 Devonian period, while an abundant vegetation spread over 

 the land, traces of no fewer than a hundred diflerent species 

 of plants having been discovered in the Old Bed Sandstone. 

 True conifers now began to appear, or at least fossil races of 

 such trees are for the first time recognissd in Devonian 

 rocks. 



The forests must have been uniformly green, for millions 

 of years were to pass before deciduous trees were to appear. 

 Many forms of insect life existed in those overgreen forests ; 

 fossil wings of insects have been found which seem even to 

 indicate by their size an exceptional wealth of insect life ; 

 for races attain large size only under favour.ible conditions. 

 Thus among several forms of May Fly we find one whose 

 wings must have had a spread of fully five inches ! Strange, 

 be it noted in passing, to find traces thus ancient certainly 

 not less than 20,000,000 of years old, of a creature whose 

 very name— the ^y)/(p»iwo>i natui-alists call it — means the 

 creature of an hour, so short is its actual life, so slight its 

 seeming hold upon existence. 



But now for the purpose of the sketch here planned we 

 need no longer consider the details of the progress and 

 development of life. We have thus far considered these 

 because they serve to show how far back, lieyoud the time 

 even when the oldest rocks were forming, we must throw 

 the beginning of life upon our earth. But so soon as we 

 have recognised this, so soon as we have understood that 

 periods to be measured by hundreds of thousand.?, if not by 

 millions of years, must have passed while the fauna and 

 flora of even the Silurian rocks were being developed, we 

 can pass onwards over stage after stage of the earth's life, 

 noting how during every stage multitudinous forms of 

 animal and \-egetable life existed. Some forms were as yet 

 in the first stages of development, others fully formed, 

 others highly developed, and others already approaching 

 the time when, having outlasted their proper era, they were 

 about to disappear. In disappearing they left the field open 

 to kindred races not descended from them hut from the 

 same progenitors, having, however, been saved from 

 extinction by such changes as fitted them for their en- 

 vironment. 



In this sense one may compare the various forms of life, 

 animal and vegetable, to the various individual representa- 

 tives of that form, among whom we recognise at one and 

 the same time the infant, the young, the middle-aged, the 

 old, and those nearing death. For species and genera as 

 well as iniUviduals have their inception, their growth, their 

 full vigour, theii' decay, and finally their death ; though 

 because the pei-iods of time necessary for the full develop- 

 ment and the eventual decay of a race are so long that the 

 lifetime of an individual (even of a longer-lasting type) is 

 usually but a second by comiiarison, we are apt to imagine 

 permanence where in reality there is only relatively long- 

 lasting development and dissolution. 



It has been because of this that men have so long been 

 led to imagine that races of plants and animals can be 

 neither developed nor destroyed, that all races must have 

 had their beginning in a process of direct creation, and can 

 only have their ending through a proce.--"S of catastrophic 

 destruction. Even when geologists began to recognise the 

 enormous duration not only of the so-called primary, 



