192 



SCIENCE. 



[Vol. II., No. 28. 



In the next succeeding formation, the true lower 

 Laurentian of Logan, the Granville series of Canada, 

 we meet with a great and significant change. It is 

 true, we liave still a predominance of gneisses which 

 may have heen fornie<l in the same manner with those 

 below them; but we find these now associated with 

 great beds of limestone and dolomite, which must 

 have been formed by the separation of calcium and 

 magnesium carbonates from the sea-water, either by 

 chemical precipitation or by the agency of living 

 beings. We have also quartzite, quartzose gneisses,' 

 and even pebble beds, which inform us of sand-banks 

 and shores. Nay, more, we have beds containing 

 graphite which must be the residue of plants, and 

 iron ores which tell of the deoxidation of iron oxide 

 by organic matters. In short, here we have evidence 

 of new factors in world-building, — of land and ocean, 

 of atmospheric decay of roclcs, of deoxidizing pro- 

 cesses carried on by vegetable life on the laud and 

 in the waters, of limestone-building in the sea. To 

 afford material for such rocks, the old Ottawa gneiss 

 must have been lifted up into continents and moun- 

 tain masses. Under the slow but sure action of the 

 carbonic dioxide dissolved in rain-water, its felspar 

 had crumbled down in the course of ages. Its pot- 

 ash, soda, lime, magnesia, and part of its silica, had 

 been washed into tlie sea, there to enter into new 

 combinations, and to form new deposits. The crum- 

 bling residue of fine clay and sand had been also 

 washed down into the borders of the ocean, and bad 

 been there deposited in beds.i 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 tlie mystery of the world 

 wlien I affirm that this great change took place, this 

 new era was inaugurated, in the midst of the Lau- 

 rentian period. 



Was not this time a fit period for the first appear- 

 ance 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 character- 

 ized 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 

 wliich 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 state, more especially in the mat- 

 ters of crystallization and the formation of dessemi- 



1 Dr. Hunt lias now in preparation for the press an important 

 paper on tbis subject, read before tbe National academy of sci- 



nated minerals by the action of heat and heated 

 water. Sandstones have tlius passed into quartzites, 

 clays into slates and schists, Jiniestones into marbles. 

 So far, metamorphism is not a doubtful question; 

 but, wlien theories of metamorphism go so far as to 

 suppose an actual change of one elemeutfor another, 

 they go beyond the bounds of chemical credibility; 

 yet such theories of metamorphism are often boldly 

 advanced, and made the basis of important conclu- 

 sions. Dr. Hunt has happily given the name ' meta- 

 somatosis' to this imaginary and impossible kind of 

 metamorphism, 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 tlie metamorphism 

 of the older crystalline rocks, it is not to this meta- 

 somatosis that I refer, and that I hold that rocks 

 which have been produced out of the materials de- 

 composed by atmospheric erosion can never, by any 

 process of metamorphism, be restored to 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 con- 

 fidence, but whicli does not apply to the more modern 

 deposits. Still, nothing in geology absolutely perishes 

 or is altogether discontinued; and it is probable, that, 

 down to the present day, the causes which produced 

 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 the typical orthoclase and horn- 

 blendic gneiss of the Laurentian, there are mica- 

 ceous, quartzose, garnetiferous, and many other kinds 

 of gneiss; and even gr.eissose rocks, which hold lab- 

 radorite or anorthite instead of orthoclase, are some- 

 times, though not accurately, included in the term. 



The Grenville series, or middle Laurentian, is suc- 

 ceeded by what Logan in Canada called the upper Lau- 

 rentian, and which other geologists have called the 

 Norite or Norian series. Here we still have our old 

 friends the gneisses, but somewhat peculiar in type; 

 and associated with thenr are great beds rich in lime- 

 felspar, — -the so-called labra<lorite and anorthite 

 rocks. Tlie precise origin of these is uncertain, but 

 tliis much seems clear; namely, that they originated 

 in circumstances in which tbe great limestones depos- 

 ited in the lower or middle Laurentian were begin- 

 ning to be employed in the manufacture, probably by 

 aqueo-igneous agencies, of lime-felspars. This proves 

 the Norian rocks to be much younger than the Lau- 

 rentian, and that, as Logan supposed, considerable 

 earth-movements had occurred between the two, 

 implying lapse of time. 



Next we have the Huronian of Logan, — a series 

 much less crystalline and more fragmentary, and 

 affording more evidence of land elevation and atmos- 

 pheric and aqueous erosion, than any 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 



