45° 



NATURE 



{Sept. 6, 1883 



down in the course of ages. Its potash, soda, lime, magnesia, 

 and part of its silica, had been washed into the sea, there to 

 enter into new combinations, and to form new deposits. The 

 crumbling residue of fine clay and sand had been also washed 

 down into the borders of the ocean, and had been there de- 

 posited in beds. 1 Thus the earth had entered into a new phase, 

 which continues onward through the geological ages; and I 

 place in your hands one key for unlocking the mystery of the 

 world when I affirm that this great change took place, this new- 

 era was inaugurated, in the midst of the I.aurentian period. 



Was not this time a fit period for the first appearance of life ? 

 Should we not expect it to appear, independently of the evidence 

 we have of the fact ? I do not propose to enter here into that 

 evidence, more especially in the case of the one well characterised 

 Laurentian fossil, Eozoon canadense. I have already amply 

 illustrated it elsewhere. I would merely say here, that we should 

 bear in mind that, in this later half of the Lower Laurentian or, 

 if we so choose to style it, middle Laurentian period, we have 

 the conditions required for life in the sea and on the land ; and 

 since in other periods we know that life was always present 

 when its conditions were present, it is not unreasonable to look 

 for the first traces of life in this formation, in which we find for 

 the first time the completion of those physical arrangements 

 which make life, in such forms of it as exist on our planet, 

 possible. 



This is also a proper place to say something of the doctrine 

 of what is termed "metamorphism." The Laurentian rocks are 

 undoubtedly greatly changed from their original itate, more 

 especially in the matters of crystallisation and the formation of 

 di -eniinated minerals by Ihe action of heat and heated water. 

 Sandstones have thus passed into quartzites, clays into slates and 

 schists, limestones into marbles. So far, metamorphism is not 

 a doubtful question ; hut, when theories of metamorphism go 

 so far as to suppose an actual change of one element for another, 

 they go beyond the bounds of chemical credibility ; yet such 

 theories of rnetam irphism are often boldly advanced, and made 

 the basis of important conclusions. Dr. Hunt has happily given 

 the name " metasoinatosis " to this imaginary and impossible 

 kind of metamorphi*m, which may be regarded as an extreme 

 kind of evolution, akin to some of those" forms of that theory 

 employed with reference to life, but more easily detected and 

 exposed. I would have it to be understood that, in speaking 

 of the metamorphi m of the older crystalline rocks, it is not to 

 this metasomatosis that I refer, and that I hold that rocks which 

 have I een produced out of the materials decomposed by atmo- 

 spheric erosion can never, by any process of metam rphism, be 

 rest ired t 1 the precise condition of the Laurentian rocks. Thus 

 there is in the older formations a genealogy of rocks, which, in 

 the absence of fossils, may be used with some confidence, but 

 which does not apply to the more medrrn deposits. Still, 

 n. thing in ge lo y absolutely perishes or is altogether discon- 

 tinued ; and it is probable, that, down to the present day, the 

 causes which pr< duced the old Laurentian gneiss, may still operate 

 in limited localities. Then, however, they were general, not 

 exceptional. It is further to be observed that the term "gneiss" 

 is sometimes of wide and even loose application. Beside ihe 

 typical orthoclase and hornblendic gneiss of the Laurentian, 

 there are micaceous, quartzose, garnetiferous, and many other 

 kinds of gneiss ; and even gneissose rocks, which hold labradorite 

 or anorlhite instead of orthoclase, are sometimes, though not 

 accurately, included in the term. 



The Grenville series, or middle I.aurentian, is succeeded by 

 what Logan in Canada called the upper Laurentian, and which 

 Olher geologists have called the Norite or Nori.111 series. Here 

 we still have our old friends the gnebses, but somewhat peculiar 

 in type; and associated with them are great beds rich in lime- 

 felspar,— the so-called labradorite and anorthite rocks. The 

 precise origin of these is uncertain, but this much seems clear ; 

 namely, that they originated in circumstances in which the great 

 limestones deposited in the lower or middle Laurentian were 

 beginning to be employed in the manufacture, probably by 

 aquco-igneous agencies, of lime-felspars. This proves the Norian 

 rocks to be much younger than the Laurentian, and that, as 

 Logan supposed, considerable earth-movements had occurred 

 between the two, implying lapse of time. 



Next we have the Huroman of Logan, — a series much less 

 crystalline and more fragmentary, and affording more evidence 

 of land elevation and atmospheric and aqueous erosion than any 



■Dr. Hunt has now in preparation for the press an important paper on this 

 subject, read bef.re the National Academy of Sciences. 



of the others. It has great conglomerates, some of them made 

 up of rounded pebbles of Laurentian rocks, and others of 

 quartz pebbles, which must have been the remains of rocks 

 subjected to very perfect erosion. The pure quartz rocks tell 

 the same tale, while limestones and slates speak also of chemical 

 separation of the materials of older rocks. The Huronian 

 evidently tells of movements in the previous I.aurentian, and 

 changes in its texture so great, that the former m iy he regard, d 

 as a comparatively modern rock, though vastly older than any 

 part of the palaeozoic series. 



Still later than the Huronian is the great micaceous series 

 called by Hunt the Mont Alban or White Mountain group, and 

 the Taconian or lower Taconic of Emmons, which recalls in 

 some measure the conditions of the Huroman. The precise 

 relations of thee to the later formations, and to certain doubtful 

 deposits around Lake Superior, can scarcely be said to he settled, 

 though it would seem that they are all older than the fossiliferous 

 Cambrian rocks which practically constitute the base of the 

 palaeozoic. 1 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 dogmatise as to the 

 precise relations of those last mentione ', or as to the precise age 

 of some disputed formations which may either be of the age of 

 the older eozoic formations, or may be peculiar kinds of palaeozoic 

 rocks modified by metamorphism. Probably 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 action or to the alteration of ordinary sedi- 

 ments. Under the treatment of another school, they grow to 

 great series of pre-Cambrian rocks, constituting va t systems of 

 formations, distinguishable from each other, not by fossils, but 

 by differences of mineral character. I have already indicated 

 the manner in which I believe the dispute will ultimately be 

 settled, and the president of ihe geological sec ion will treat it 

 nine fully in his opening address. 



After the solitary appearance of Eozoon in the Laurentian, 

 and of a few u certain forms in the Huronian and Taconian, we 

 find ourselves in the Cambrian, in the presence of a nearly 

 complete invertebrate fauna of protozoa, polyp, echinoderms, 

 mollusks, and Crustacea; and this not confined to one locality 

 merely, but api arently extended simuhaneou ly through rut tie 

 ocean. This sudden incoming of animal life, along with the 

 subsequent introduction of successive groups of invertebrate, 

 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 v^ successive creations. In an 

 address delivered at the Detroit meeting of the Association in 

 1875, I endeavoured to ^et forth the facts as to this succession, 

 and the general principles involved in it, and to show the 

 insufficiency of the theories 1 f 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 positi n with respect to these great 

 questions that we were in at that time, — a singular proof of the 

 impotency of that deductive method of reasoning which has 

 become fashionable among naturalists of late. Yet the discus- 

 sions 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 scientific 

 evolutionists have met the extreme views of such men as 

 Romanes, Haeckel, Lubbock, and Grant Allen. It may be 

 useful to note some of the e as shedding a little light on this 

 dark corner of our unsolved problems. 



It has been urged, on the side of rational evolution, that 

 this hypothe.-is does not profess to give an explanation of the 

 absolute origin of life on our planet, or even of the original 

 organisation 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 

 living froui 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 swarm with s warmers." How vast is the gap in 

 our knowledge and our practical pow er implied in this admission, 

 which must, however, be made by every mind not absolutely 



