August 26, 1897] 



NA TURE 



W 



while Hall, Emmons and others, working upon these lines, 

 were actively engaged in building up a similar classification of 

 the Paleozoic rocks of the Eastern States of the American 

 Union. The Silurian and Cambrian had, in fact, but just been 

 reclaimed from what Murchison speaks of as the " vast un- 

 classified heaps of greywacke " or " transition limestones." 



It would have been quite appropriate at this date to relegate 

 all underlying and more or less completely crystalline rocks to 

 the "Primary," or "Primitive," or "Azoic," but such a 

 solution fortunately did not recommend itself to Logan. 



It was along the Ottawa Valley, in 1845, that the rocks sub- 

 sequently classed under the Laurenlian and Huronian systems 

 were first examined in some detail. In that year Logan met 

 with and accurately described, severally, rocks which we now 

 refer to (i) The Fundamental Gneiss; (2) The Grenville 

 Series ; and (3) The Huronian. He speaks of the rocks of the first 

 class as being in the main syenitic gneisses " of a highly crystal- 

 line quality, belonging to the order which, in the nomenclature of 

 Lyell, is called metaniorphic instead of primary, as possessing 

 an aspect inducing a theoretic belief that they may be ancient 

 sedimentary formations in an altered condition." In what we 

 now call the Grenville Series, he describes the association of 

 crystalline limestones and interbedded gneisses, adding that it 

 appeared to be expedient to consider this mass as a separate 

 metamorphic group, supposed to be newer than the last. Of 

 the Huronian, the relations were at that time left undeter- 

 mined, although it is observed that its beds hold pebbles of the 

 underlying rocks, here the Fundamental Gneiss. 



The following season was spent by Logan, and by his assistant 

 Murray, on the north shore of Lake Superior, Thunder Bay 

 and its vicinity being one of the regions especially examined. 

 Without enumerating particular localities, it may be stated that 

 Logan there grouped the rocks met with as follows, beginning 

 with the lowest ; the column added (m the left giving the present 

 nomenclature of the several series defined : — 



Laurentian .. 

 Huronian .. 



Animikie 

 Keweenawan 



/ I. Granite and syenite. 

 \ 2. Gneiss. 

 3. Chloritic and partly talcose 

 and conglomerate slates 

 [schists]. 

 . 4. Bluish slates or shales inter- 

 stratified with trap. 

 5. Sandstones, limestones, in- 

 durated marls and con- 

 glomerates, interstratified 

 with trap. 

 It is not distinctly stated that No. 3 rests unconformably on 

 the older rocks, but the observation that granitic boulders were 

 found in it, leads to the belief that such unconformity was 

 assumed. Murray, however, supposed the junction as seen on 

 the Kaministiquia to be conformable, and unites the first three 

 subdivisions, as above given, in one series. 



Logan further states, still referring to the same region, that the 

 " chloritic slates [schists] at the summit of the older rocks on 

 which the volcanic formations rest unconformably, bear a strong 

 resemblance to those met with on the upper part of Lake 

 Temiscaming on the Ottawa, and it appears probable that they 

 will be found to be identical." 



It will thus be observed that the progress in classification 

 made, up to this date at least, entirely accords with the results 

 of the latest investigations. The identity of the rocks placed 

 third in the table with those of the Upper Ottawa was more than 

 conjectured, and the existence of a great stratigraphical break at 

 the base of what is now known as the Animikie was clearly 

 recognised. The several formations were merely described. No 

 specific names were given to them at this time by Logan, and it 

 is further stated that the age of the highest formations (Animikie 

 and Keweenawan) was in doubt, although some reason was found 

 to support Houghton's (then Slate Geologist of Michigan) view 

 (or what was believed to be his view), that these formations are 

 lower than the Potsdam, or "lowest fossiliferous formation." 



In 1847 and 1848, investigations were continued along the 

 north shore of Lake Huron, of which the characteristic rocks 

 are, it is stated, believed to form a single system. They are 

 described as in part sedimentary (quartzites, conglomerates, (Sec. ), 

 and in part igneous (greenstones), the latter being both interposed 

 between the sedimentary beds and intrusive. The " slates " are 

 particularly characterised by Murray as often chloritic, epidotic, 

 and micaceous, and would now, of course, be more specifically 

 termed schists. 



NO. 1452. VOL. 56] 



Writing in 1849 ("Report on the North Shore of Lake 

 Huron"), however, and later, in a communication presented to 

 this Association in 1851, Logan, although still recognising the 

 manifest unconformity at the base of the Animikie, speaks col- 

 lectively of the " Copper-bearing Rocks" of Lake Superior and 

 Huron, including under this general term what are now known 

 as the Huronian, Animikie, and Keweenawan series, and adds 

 that it is " highly probable " that all these are approximately 

 equivalent to each other, and to the Cambrian of the British 

 Islands. 



In the Report for 1852-53 (published 1854), the name 

 Laurentian was adopted for what had been previously designated 

 merely as the " metamorphic series," and in the geological 

 sketch printed in Paris in connection with the Exhibition of 

 1855 (which* follows next in order of publication), this system is 

 stated to consist almost exclusively of much altered and disturbed 

 sedimentary beds. It is also, however, made to include some 

 recognised intrusives, such as granite and syenites, forming parts 

 of the mass, as well as the Labradorite rocks, which were after- 

 wards for a time named Upper Laurentian, and to which further 

 allusion will be made in the sequel. The name Laurentian is 

 here, therefore, first employed exactly in the sense of the term 

 " Basement Complex," introduced l^ng afterwards, but under 

 the distinct idea that most of the rocks are altered sediments, 

 from which certain intrusive masses were not clearly separable. 



In the same pul^lication, the overlying series of Lakes Huron 

 and Superior, including the Huronian proper, the Animikie and 

 the Keweenawan, were collectively spoken of as the "Huronian 

 or Cambrian system." These rocks are described as lying dis- 

 cordantly on the Laurentian, and as intervening between it and 

 the lowest known fossiliferous strata. There being no other 

 recognised place for such rocks in the scheme of the day, they 

 are consequently supposed to represent the Lower Cambrian of 

 Sedgwick. 



It is unnecessary to follow in order the investigations carried 

 on for a number of subsequent years, but reference may now be 

 made to the " Geology of Canada," of 1863, in which all previous 

 results of the Survey to that date were collected and systematised. 

 In this volume, after stating that Hall's nomenclature of the 

 Palaeozoic rocks in the State of New York had been adopted un- 

 changed for the adjacent Canadian territory, "in the interestsof 

 unity of plan for future researches," Logan writes : — "To the 

 Azoic rocks no local names have yet been applied in any part of 

 America except in Canada," and adds: — "The names of the 

 Laurentian and Huronian systems or series, which we have been 

 accustomed to apply to them, are allowed to remain unchanged, 

 particularly as they have been recognised abroad, and have been 

 made by other geologists a standard of comparison both in 

 America and Europe." 



In Chapter V. of this volume the " Upper Copper-bearing 

 Rocks of Lake Superior " are separately treated, and are 

 recognised as comprising two groups which are stated to overlie 

 the Huronian unconformably. These groups are those now 

 known as the Animikie and Keweenawan, 



There can be no doubt about the classification intended at this 

 time, and the rocks are correctly laid down on the atlas prepared 

 to accompany the volume, but in consequence of an unfortunate 

 error in the geographical description of the distribution of the 

 Huronian about Thunder Bay, that arose in 1846 and was re- 

 peated in 1863, several later investigators have been led to regard 

 the rocks of the " Upper Copper-bearing Series" as those of 

 Logan's typical Huronian, and to suppose that when examining 

 these rocks they were dealing with those intended to be classed as 

 Huronian. Irving, Winchell and others have adopted this mis- 

 taken view, which it is particularly necessary to refer to here, as 

 it has been the chief cause of ail subsequent misapprehension in 

 regard to the " Original Huronian." ^ 



1 As already stated, the relations of the principal rock-series of the vicinity 

 of Thunder Bay had been correctly outlined in 1846, although the series had 

 not at that time been named. The Kaministiquia River section had been 

 examined by Murray, who also correctly described the distribution of the 

 series there, stating that the "granite, syenite, gneiss, micaceous and 

 chloritic schist" (Laurentian and Huronian) find their southern limitona 

 line running from the falls on that river to the "' head of Thunder Bay," while 

 the " Upper Slates (Animikie) rest upon them and occupy the country be- 

 tween such a line and Lake Superior " ('' Report of Progress," 1846-47, p. 51). 

 In combining his own results with those of Murray, Logan describes the 

 southern line of the granite, gneiss, and chloritic slates as " commencing in 

 the vicinity of Fort William, "or at the ;«o«M of the Kaministiquia, although 

 the falls, at which this line h.-»d been determined by Murray, are some twenty 

 miles up the river. Proceeding (op. cit. p. 25) to describe the extent of the 

 " superior trappean formations ' (Animikie and Keweenawan), he then reverts 

 to the line previously stated, making these rocks to terminate locally where 



