400 



NATURE 



[August 26, 1897 



the Grenville Series of the eastern and the Hnronian of the 

 •western province of the Protaxis. 



To what extent the above sulsdivisions of the Archaean may 

 be legitimately employed in other parts of the continent, more 

 or less remote from the Protaxis, remains largely a question for 

 future investigation. In the southern part of New Brunswick, 

 however, the resemblance of the Archcean to that of the typical 

 region is so close that there can be little risk of error in apply- 

 ing the same classificatory names to it. The Fundamental 

 Gneiss is there in contact with a series comprising crystalline 

 limestones, quartzites, and gneissic rocks, precisely resembling ' 

 •those of the Grenville Series. Later than this is a great mass 

 ■of more or less highly altered rocks, chiefly of volcanic origin, . 

 comprising felsites, diorites, agglomerates, and schists of various 

 kinds, like those of the typical Huronian. The existence of 

 this upper group correlatively with that representing the Gren- 

 ville Series, constitutes an argument, so far as it goes, for the 

 separateness of these two formations in the general time-scale. 

 All these Archrean rocks of New Brunswick are distinctly un- j 

 -conformable beneath fossiliferous beds regarded by Matthew as [ 

 older than Cambrian. | 



In the Cordilleran region of Canada, again, a terrane is found i 

 lying unconformably beneath the lowest rocks possibly referable 

 to the Cambrian, evidently Archrean, and with a very close 

 general resemblance to the Grenville Series. To this the local , 

 name Shuswap Series has been applied, and a thickness of at 

 least 5000 feet has been determined for it in one locality. It 

 x;onsists of coarsely crystalline marbles, sometimes spangled 

 with graphite and mica, quartzites, gneisses, often highly 

 calcareous or quartzose, mica schists, and hornblendic gneisses. 

 With these is a mvich greater mass of gneissic and granitoid 

 rocks, like those of the Fundamental Gneiss of the Protaxis, 

 and the resemblance extends to the manner of association of the 

 two terranes, of which, however, the petrographical details 

 Temain to be worked out {cf. Annual Report Geological Survey 

 of Canada, 1888-89, p. 29 B.). 



While it is true that a resemblance in lithological character, 

 like that existing between the Grenville and Shuswap Series, 

 far remote from each other geographically, may mean only that 

 rocks of like composition have been subjected to a similar meta- ! 

 morphism, both the series referred to are separated above by an j 

 -unconformity from the lowest beds of the Palreozoic, and there 

 is thus sufficient evidence to indicate at least a probability of 

 their proximate identity in the time-scale. In Scotland, an 

 analogous series, and one apparently similarly circumstanced, 

 «eems to occur in the rocks of Gairloch and Loch Carron 

 ■{cf. Geikie, "Ancient Volcanoes of Great Britain," vol. i. 

 p. 115). 



Particular attention has been directed throughout to the 

 southern part of the continental Protaxis in Canada. In this 

 region it happened that the Archrean rocks and those resting 

 upon them were originally studied under exceptionally favour- 

 able conditions, for ever since the great revolution which suc- 

 ceeded Huronian time, the region is one which has remained 

 almost stable. Selwyn and N. H. Winchell have particularly 

 insisted on the importance of the stratigraphical break which 

 here defines the Archisan above. It is not everywhere so well 

 marked, for in the Appalachian province and in the country to 

 the south of the great lakes, in Wisconsin and Michigan, re- 

 peated subsequent earth-movements have flexed and broken the 

 older strata against the base of the table-land of the Protaxis. 

 It is not from these districts, subjected to more recent and fre- 

 quent disturbance, that the ruling facts of an earlier time may be 

 most easily ascertained. Much careful and conscientious work 

 has been devoted to them, but it is largely, I believe, because 

 of the attempt to apply, for purposes of general classification, 

 the still unsettled and ever-changing hypotheses derived from 

 such more complicated tracts that so much confusion has 

 been introduced in regard to the Archaean and early Palaeozoic 

 rocks. 



If the unconformity closing Archaean time in the vicinity of 

 the Great Lakes had been observed only in that region, it might 

 be regarded as a relatively local phenomenon ; but subsequent 

 -observations, and more particularly those of the last few years, 

 -due to Bell, McConnell, Tyrrell, and Low, show that rocks 

 -evidently representing the Animikie and ' Keweenawan, and 

 practically identical with those of Lake Superior in general 

 lithological character, recur in many places almost throughout 

 the whole vast area of the Protaxis, on both sides of Hudson 



Bay, and northward to the Arctic Ocean, resting upon the 

 Archaean rocks always in complete discordance, and lying 

 generally at low angles of inclination, although often affected 

 by great faults. The surface upon which these rocks have been 

 deposited is that of a denudation-plane of flowing outline, not 

 diff"ering in any essential respect from that characterising parts 

 of the same great plateau where there is no evidence to show 

 that any deposition of strata has occurred since Archtean time. 

 Mr. Low, indeed, finds reason to believe that even the great 

 valleys by which the Archaean plateau of Labrador is trenched 

 had been cut out before the general subsidence which enabled 

 the laying down of Animikie rocks upon this plateau to begin. 

 The area over which these observations extend, thus in itself 

 enables us to affirm that the unconformity existing between the 

 Animikie or Keweenawan (as the case may be) and the Archaean 

 is of the first order {cf. Selwyn, Science, February 9, 1883). It 

 may be compared with that now known to occur between the 

 Tgrridonian of Scotland and the underlying rocks there, and is 

 evidenced by similar facts. 



If the structural aspects of the Archaean rocks of the Protaxis 

 are considered, the importance of this gap becomes still more 

 apparent. We find long bands of strata referable to the 

 Huronian and Grenville Series, occupying synclinal troughs, 

 more or less parallel to each other and to the foliation of the 

 Fundamental Gneiss, the strata, as well as the foliation, being 

 in most cases at high angles, vertical, or even reversed. This 

 structure is precisely that which would be discovered if a great 

 mountain system, like that of the Alps, were to be truncated on 

 a plane sufficiently low. Analogy thus leads to the belief that 

 the Protaxis was originally, as Dana has suggested, a region of 

 Appalachian folding, differing only from more modern examples 

 of mountain regions of the same kind in its excessive width, 

 which is so great as to render it difficult to conceive that crustal 

 movements of sufficient magnitude to produce it could have 

 occurred at any one period. It is thus, perhaps, more probable 

 that successive and nearly parallel flexures of the kind, separated 

 by long intervals of rest, piled range upon range against the 

 central mass of the protaxial buttress subsequent to the Huronian 

 period. In any case, the rugged mountain region brought 

 into existence when the corrugation still evidenced by its re- 

 maining base occurred, was subsequently reduced by denudation 

 to the condition of an undulating table-land such as has been 

 named a "peneplain" by W. M. Davis — a surface approxi- 

 mating to a base-level of erosion. All this was accomplished 

 after the close of the Huronian period, and before that time at 

 which the first beds of the Animikie were laid down correlatively 

 with a great subsidence. It would be difficult to deny that the 

 time thus occupied may not have been equal in duration to that 

 represented by the whole of the Palaeozoic. 



If we approach this ruling unconformity from above, in the 

 region of the Protaxis, we find the Animikie and Keweenawan 

 rocks uncrystalline, except when of volcanic origin, and re- 

 sembling in their aspect the older Palaeozoic sediments, but 

 practically without characteristic organic remains so far as 

 known. In order to bring ourselves into relation with the 

 ascertained palaeontological sequence, it is necessary to go 

 further afield, and in so doing we lose touch, more or less com- 

 pletely, with the stable conditions of the Archaean platform, 

 and are forced to apply indirectly such facts as it may be pos- 

 sible to ascertain in regions which have suffered more recent 

 and complicated disturbance. It is thus not surprising that the 

 taxonomic position of the Animikie and Keweenawan have been 

 the subject of much controversy. It is not germane to the pre- 

 sent discussion to enter at any length into this question, nor into 

 the value of the unconformity which appears to e-^ist between 

 these two series. They have been classed collectively by 

 Selwyn, N. H. Winchell, and others as Lower Cambrian, 

 and are provisionally mapped as such by the Canadian 

 Survey. It is believed to be more in accordance with the 

 general principles of geological induction to refer these rocks 

 above the great unconformity to the Cambrian, for the time 

 being at least, than to unite them with the Huronian under any 

 general term, or to erect a new system in which to place them. 

 In so doing it has been assumed that the Cambrian is the lowest 

 system of the Palaeozoic, but of late years the position has been 

 taken by good authorities that the true base of the Cambrian is 

 to be found at the Olenellus zone ; and while it appears very 

 probable that, when fossils are found in the Animikie, they may 

 be referable to this zone, the adoption of such an apparently 



NO. 1452, VOL. 56] 



