398 



NA TURE 



[August 26, 1S97 



The temporary grouping of the Huronian prc^per with the 

 " Upper Copper-bearing Series" (Animikie and Keweenawan), 

 on the grounds already explained, as "Huronian or Cambrian," 

 together w ith the employment (proper enough at the date) of the 

 term " slates " for rocks that would now be named schists, further 

 assisted in giving colour to the erroneous view just referred to. 



In a second geological sketch of Canada, printed in Paris at 

 the time of the International Exhibition of 1867, the same classi- 

 fication is maintained, but to it is added the Upper Liuirentian 

 or Labradorian. This sketch was actually written by Hunt, but 

 it was an official publication correctly representing the views held 

 at that time, and may be accepted as Logan's last word on the 

 subject. As thus defined and established, he left the Laurentian 

 and Huronian systems. 



In so far as the stratigraphical relations of the Laurentian, 

 Huronian, and " Upper Copper-bearing Series" are concerned 

 (leaving out of consideration the Labradorian), it is thus mani- 

 fest that the conclusions originally formed from actual study on 

 the ground were those finally held by Logan. The reference 

 for a time of the Huronian proper and the "Upper Copper- 

 bearing Series " together to the Lower Cttmbrian, meant only 

 that, as then undeistotd, there was no other systematic position 

 recognised to which they could be assigned. That a great un- 

 conformity existed between these two systems was never doubted, 

 but for some years Lrgan was not prepared to take the bold 

 position of constituting a separate Huronian system beneath the 

 lowest Cambrian ; he was, on the contrary, anxious, if possible, 

 to bring the Canadian section within the lines established in the 

 classic region studied by Sedgwick and Murchison. The intro- 

 duction of new systematic terms was at that time considered 

 somewhat seriovisly. When eventually compelled to take this 

 step (in 1857), he confined the name Huronian to rocks ante- 

 dating the great break at the base of the " Upper Copper- 

 bearing Series " (Animikie), embracing those first seen by him 

 on the Upper Ottawa and on Lake Huron, with their repre- 

 sentatives elsewhere, under this new s) stem. 



In so far as nomenclature goes, Logan thus certainly modified 

 his original application of the name Huronian ; it was not, how- 

 ever, as has been contended, to create an " extended Huronian," 

 but on the contrary to restrict the name to rocks beneath the 

 great unconformity at the base of the Animikie. The change 

 was necessitated by the progiess of investigation and by the 

 recognition of an upper division of the "Azoic," beneath any- 

 thing that could legitimately be classed as Cambrian. It was 

 made by the author himself, and involved no departure from the 

 law of priority or from any other acknowledged rule. In finally 

 eliminating these upper rocks from his Huronian system, he was 

 no doubt influenced by Whitney's criticisms of 1857 {Avi. Jozirii. 

 Set., vol. xxiii., May 1857), which were in part correct, although 

 largely devoted to the very conservative contention that all 

 stratified rocks below the great break were inseparable, and 

 should be included in an "Azoic System." This influence may 

 be traced in an important paper, of but three pages, communi- 

 cated to the American Association for the Advancement of 

 Science a few months later than the date of that above referred 

 to, in which, while the name Huronian is reaffirmed for the 

 rocks of Lake Huron and Lake Temiscaming, which are taken 

 as typical of the system, nothing further is said of those now 

 known as Animikie and Keweenawan. 



In the summary volume of 1863, to which allusion has already 

 been made, the existence of an Upper Laurentian, Labradorian 

 or Norian Series was first tentatively indicated in a supple- 

 mentary chapter. It is unnecessary to follow here the history 

 of the rocks so classed, for the supposed series has not stood the 

 test of later discussion and research, due chiefly to Selwyn and 

 Adams. The apparently stratified rocks often included in it 

 are now understood to be foliated eruptives. The recognition 

 achieved by this and by other more or less hypothetical series 



he had said the older rocks began. In recasting the earlier observations for 

 the volume of 1863 (no further work having meanwhile been done at this 

 place), Logan is thus naturally led to state that the Huronian (i.e. the 

 ." Chloritic Slates") occiipus the coast east of the Kaniinistiqiiia, whereas 

 this coast, for ten or eleven miles, is actually occupied by Animikie rocks. 

 Subsequent investigators, inspecting this coast-line with the volume of 1863 

 as a guide, very naturally thus assumed that they were examining Logan's 

 " typical Huronian," or a part of it. It is in consequence only of a too con- 

 sistent adhesion to this misunderstanding, that it has been found necessary 

 to speak of an "Upper Huronian," and refer to an "inter-Huronian " un- 

 conformity. The so-called Upper Huronian is no part of the system as 

 understood by the Canadian Survey. One cannot fail to note, in reading 

 much that has been written i^n this subject, that the importance of the great 

 unconformity at the base of the Animikie was realised only after a new classi- 

 fication had been adopted, in which it had practically been ignored. 



NO. 1452, VOL. 56] 



about this time maybe traced to the brilliant chemico-geological 

 theories advanced by Hunt, previous to the general acceptance 

 of modern petrographical methods. 



In a similar manner, and very justly so, Logan, as a field 

 geologist, was influenced by the views held by Lyell in the early 

 editions of his "Principles," to accept without reservation the 

 foliation of crystalline rocks as indicative of original bedding. 

 This was, at the time of his early researches and thereafter for 

 many years, the accepted view, although Dana, in a paper read 

 before the American As.sociation for the Advancement of Science 

 in 1843, had already held that the schistose structure of gneiss 

 and mica-slate was insufficient evidence of sedimentary origin ; 

 and Darwin, a few years later, had published his " Geologicai 

 Observations," including a remarkable chapter on cleavage and 

 foliation, in which he advocated a similar view. No such 

 doctrine, however, achieved general recognition until long after- 

 wards, while that class of facts remaining to be determined 

 chiefly by the microscope, which may be included under the 

 term "dynamic metamorphism," were wholly unknown and 

 unforeseen. 



In admitting that chemical, metamorphic, and uniformitariar> 

 hypotheses were thus given, in turn, undue weight, it is not to 

 be assumed that the advances made under these hypotheses have 

 been entirely lost ; it has been necessary only to retreat in part 

 in each instance, in order to fall again into the more direct 

 road. 



In late years, modern microscopical and chemical methods of 

 research have been applied to the ancient crystalline schists of 

 Canada— the older work has been brought under review, and 

 new districts have been entered upon with improved weapons. 

 Here, as in other parts of the world, investigations of the kind 

 are still in active progress ; finality has not been reached or> 

 many points, but the explanation of others has been found. One 

 advance which deserves special mention is the recognition of the 

 fact that a great part of the Huronian is essentially composed of 

 contemporaneous volcanic material, effusive or fragmental. This- 

 was first clearly stated by Canadian geologists, but has only 

 become generally admitted by degrees, in opposition to pre- 

 valent theories of metamorphism and cosmic chemistry. 



The first opportunity of studying these Archiean rocks in 

 detail, under the new conditions, fell to Dr. A. C. Lawson, then 

 on the Staff of the Canadian Survey, in the vicinity of the Lake 

 of the Woods and elsewhere to the west of Lake Superior. Ii> 

 that part of the Protaxis, the Laurentian appears to be repre- 

 sented only by the Fundamental Gneiss, and the Huronian, by 

 a series to which a local name (Keewatin) was appropriately 

 given, ^ but which is now known to differ in no essential respect 

 from many other developments of the same system. The 

 Huronian stands generally in compressed folds, and along the 

 line of junction the gneisses are related to it in the manner of ar> 

 eruptive, penetrating its mass and containing detached fragments- 

 from it. The same or very similar relations have since beer* 

 found to occur in many other places. 



Arguing from observations of the kind last mentioned, it was- 

 too hastily assumed by some geologists that the Laurentian as a 

 whole is essentially igneous, and later in date than the Huronian. 

 The conditions are, however, not such as to admit of an un- 

 qualified belief of this kind, even in regard to the Fundamental 

 Gneiss. We may go so far as to assume that these rocks 

 (occupying as they do much the larger part of the entire Protaxis) 

 constitute a great " batholitic " mass of material at one time 

 wholly fluent ; but even on this hypothesis some primitive floor 

 must have existed upon which the Huronian and the similarly 

 circumstanced Grenville Series were laid down, and no such 

 enormous substitution can have obtained as to result in the 

 replacement of the whole of this floor by exotic material.'- It 

 seems much more probable that but limited tracts of the Funda- 

 mental Gneiss have passed into a fluent condition when at great 

 depths in the earth's crust, and various arguments may be 

 adduced in favour of a belief that the observed lines of contact 

 might be those along which such fusion would be most likely to 

 occur. -^ Moreover, the Huronian in many and widely separated 

 localities is found to contain water- rounded fragments of syenitic, 



1 In the Archaean, local names are particularly useful, inasmuch as. 

 correlation must proceed on lithological and stratigraphical data, more or 

 less uncertain when extended to wide areas, even in the case of the older and 

 more homogeneous strata of the earth's crust. 



2 For analogous phenomena of much later date geologically, see Annual 

 Report Geological Survey of Can-ida, 1886, p. 11 B. 



3 Hypotheses on this subject are well summarised by Van Hise. Annual 

 Report U.S. Geol. Survey, 1894-95, p. 749. 



