AaousT 17, 18S3.] 



SCIENCE. 



193 



quartz rocks tell the same tale, while limestones ami 

 slates speak also of chemical separation of the mate- 

 rials of oilier rocks. The Hiironian eviilenily tells of 

 movements in the previous Laurentian, and changes 

 in its texture so great, that the former may he 

 regarded as a comparatively modern rock, though 

 vastly older than any part of the paleozoic series. 



Still later than the Huronian is the great mica- 

 ceous series called by Hunt the Mont Alhan or AVhite 

 Mountain group, and the Taconian or lower Tnconic 

 of Emmons, which recalls in some measure the con- 

 ditions of the Huronian. The precise relations of 

 these to the later formations, and to certain donbtful 

 deposits around Lake Superior, can scarcely be said 

 to be settled, though it would seem that they are all 

 older than the fossiliferous Cambrian rocks which 

 practically constitute the base of the paleozoic. I 

 have, I may say, satisfied myself, in regions which I 

 have studied, of the existence and order of these 

 rocks as successive formations, though I would not 

 dogmatize as to the precise relations of those last 

 mentioned, or as to the precise age of some disputed 

 formations which m.ay either be of the age of the 

 older eozoic formations, or may be peculiar kinds of 

 paleozoic rocks modified by metamorphism. Prob- 

 ably neither of the extreme views now agitated is 

 absolutely correct. 



After what has been said, you will perhaps not be 

 astonished that a great geological battle rages over 

 the old crystalline rocks. By some geologists they 

 are almost entirely explained away, or referred to 

 igneous acticm or to the alteration of ordinary sedi- 

 ments. Under the treatment of another school, they 

 grow to great series of pre-Cambrian rocks, constitut- 

 ing vast systems of formations, distinguishable from 

 eacli other, not by fossils, but by differences of min- 

 eral character. I have already indicated the manner 

 in which I believe the dispute will ultimately be set- 

 tled, and the president of the geological section will 

 treat it more fully in his opening address. 



After the solitary appearance of Eozoon in the 

 Laurentian, and of a few uncertain forms in the Hu- 

 ronian and Taconian, we find ourselves in the Cam- 

 brian, in the presence of a nearly complete invertebrate 

 fauna of protozoa, polyps, echinoderms, mollnsks, 

 and Crustacea; and this not confined to one locality 

 merely, but apparently extended simultaneously 

 throughout the ocean. This sudden incoming of 

 animal life, along with the subsequent introduction 

 of successive groups of invertebrates, and finally of 

 vertebrate animals, furnishes one of the greatest of 

 the unsolved problems of geology, which geologists 

 were wont to settle by the supposition of successive 

 creations. In an address delivered at the Detroit 

 meeting of the association in ISl'i, I endeavored to 

 set forth the facts as to this succession, and the gen- 

 eral principles involved in it, and to show the insuf- 

 ficiency of the theories of evolution suggested by 

 biologists to give any substantial aid to the geologist 

 in these questions. In looking again at the points 

 there set forth, I find they have not been invalidated 

 by subsequent discoveries, and that we are still nearly 

 in the same position with respect to these great ques- 



tions that we were in at that time, — a singular proof 

 of the iinpotency of that deductive method of reason- 

 ing which has become fashionable among naturalists 

 of late. Yet the discussions of recent years have 

 thrown some additional light on these matters; and 

 none more so than the mild disclaimers with which 

 my friend Dr. Asa Gray and other moderate and sci- 

 entific evolutionists have met the extreme views of 

 such men as Homanes, Haeckel, Lubbock, and Grant 

 Allen. It may be useful to note some of these aa 

 shedding a little light on this dark corner of our 

 unsolved problems. 



It has been urged on the side of rational evolution, 

 that this hypothesis does not profess to give an expla- 

 nation of the absolute origin of life on our planet, 

 or even of the original organiz.alion of a single cell or 

 of a simple mass of protoplasm, living or dead. All 

 experimental attempts to produce by synthesis the 

 complex albuminous substances, or to obtain the liv- 

 ing from the non-living, have so far been fruitless; 

 and, indeed, we cannot imagine any process by which 

 such changes could be effected. That they have been 

 effected we know; but the process employed by their 

 maker is still as mysterious to us as it probably was 

 to him who wrote the words, ' And God said let the 

 waters swann with swarmers.' How vast is the gap 

 in our knowledge and our practical power implied in 

 this admission, which must, however, be made by 

 every mind not absolutely blinded by a superstitious 

 belief in those forms of words which too often pass 

 current as philosophy! 



Uut if we are content to start with a number of 

 organisms ready made, — a somewhat humllialing 

 start, however, — we still have to ask. How do these 

 vary so as to give new species? It is a singular illu- 

 sion in this matter, of men who profess to be believ- 

 ers in natural law, that variation may be boundless, 

 aindess, and fortuitous, and th.at it is by spontaneous 

 selection from varieties thus produced that develop- 

 ment arises. But surely the supposition of mere 

 chance and magic is unworthy of science. A'.arieties 

 must have causes, and their causes and their effects 

 must be regidated by some law or laws. Now, it is 

 easy to see that they cannot be caused by a mere in- 

 nate teiulency in the organism itself. Every organism 

 is so nicely equilibrated, that it has no such sponta- 

 neous tendency, except within the limits set by its 

 growth and the law of its periodical changes. There 

 may, however, be equilibrium more or less stable. I 

 believe all attempts hitherto made have failed to ac- 

 count for the fixity of certain, n.ay, of very many, 

 types throughout geological lime; but the mere con- 

 sideration that one may be in a more stable state of 

 equilibrium than another so far explains it. A rock- 

 ing stone has no more spontaneous teiulency to move 

 than an ordinary bowlder, but it may be made to 

 move with a touch. So it probably is with organ- 

 isms. But, if so, then the causes of variation are 

 external, .as in many cases we .actually know them to 

 be; and they must depend on instability or change 

 in surroundings, and this so arranged as not to he too 

 extreme in amount, and to operate in some determi- 

 nate direction. Observe how remarkable the unity 



