ROCKS OF THE ATLANTIC COAST OF CANADA, ETC. 801 



II. The Hcronian System. 



In the typical area of Lake Huron, as originally described by 

 Logan and Murray *, this system rests unconformably on the Lower 

 and Middle Laurentian, and presents a great contrast in point of 

 mineral character to these formations. It is comparatively little 

 disturbed, and is clastic rather than crystalline in character. This 

 point has been well insisted upon by Dr. Bonney and by Mr. Irving 

 in recent papers f. Further, its conglomerates contain pebbles of 

 Laurentian rock in the same crystalline state in which these rocks 

 are found at present. It consists chiefly of quartzites, conglomer- 

 ates of different kinds, limestone, and slates, sometimes chloritic, 

 with interbedded diorite. Without discussing those more or less 

 crystalline rocks west of Lake Superior and in the Appalachian 

 region which have been by Logan himself and later authors identi- 

 fied with the Huronian, and which may, in part, belong to the 

 interval between the Huronian and Laurentian or to the upper beds 

 of the latter, or may even be later sediments in an altered state, we 

 may attend at once to the beds which on the Atlantic coast succeed 

 the Laurentian. We may remark, however, that, associated with 

 the Huronian at the west of Lake Superior and extending thence 

 northwards to Hudson's Bay and the Arctic sea, are the dark slates, 

 sandstones, &c. constituting the Ainimike series of Hunt. Whether 

 these constitute an upper member of the Huronian or a distinct for- 

 mation does not certainly appear. It is, however, certain that this 

 formation is very widely distributed, especially in the north $. It is 

 also to be observed that many of the bedded rocks of the Huronian 

 are really of volcanic origin, being bedded volcanic ashes or muds in 

 an altered state §. 



In Newfoundland the older slate-series of Jukes ||, which Murray 

 originally called the intermediate series, but afterwards mapped as 

 Huronian, consists, in ascending order, of quartzites with diorites and 

 jaspery bands, slate- conglomerate, green, purple, and red slates, 

 and dark-brown or blackish slates. In the upper part of this 

 or the lower part of the next group are the worm-burrows 

 known as Arenicolites sj^nraUs and the uncertain fossils described 

 by Billings as Aspidella. The lithological correspondence here 

 between Newfoundland and Lake Huron is very close, and is 

 increased by the fact that a series of red sandstones and con- 

 glomerates, the Kewenian of the West and the upper Huronian or 

 Signal-HiU beds of Jukes and Murray, overlie the typical Huronian 

 in both districts %. 



* Geology of Canada, 1863. 



t Anniversary Address, 1886. Amer. Journ. of Science, 1887. 



I Gr. M. DaAvson, " Notes on northern part of Dominion of Canada," Geol. 

 Survey, 1887, p. 8 ; Dr. E. Ball, " Eeport on Hudson Bay, 1877 to 1885," Geol. 

 Survey of Canada, 



§ Dawson, ' Canadian Naturalist,' 1857 ; Nicholson, Quart. Journ. Geol. 

 Soc. 1873 ; G. M. Dawson, Geol. Mag. 1875. 



II Eeport on Newfoundland, 1843. 

 ^ Geology of Newfoundland, 1881. 



