32 THE HURONIAN. 



foundland Signal-Hill rocks, and of the Kewenian series of the west. 

 I have been informed by the late Mr Irving that " an obscure Lingu- 

 loid shell " has been found in the quartzite of south-western Minnesota, 

 a formation which he regarded as probably below the Kewenian, and 

 possibly even Huronian.* These facts render it possible that an Upper 

 Huronian series containing precursors of the Cambrian fauna may yet 

 be recognised, or possibly a new intermediate system to be designated 

 by some other name.f It will also be observed that, like the typical 

 Huronian, such series, whether Huronian or Kewenian or intermediate, 

 will be common to the coastal and interior regions, thus diflfering from 

 the Middle Cambrian and agreeing with the recognised Lower Cam- 

 brian. 



IX. THE LAURENTIAN. 

 It is, I think, becoming more and more evident that in every part 

 of the world the oldest rocks exposed are of the nature of orthoclase- 

 gneisses associated with various kinds of crystalline schists, and locally 

 with quartzites and limestones. This statement applies with equal 

 force to the Acadian Provinces of Canada and to Western Europe. 

 In these districts, however, the old Laurentian substratum is repre- 

 sented, not by great continuous areas, as in the interior of North 

 America, but by rugged islets and ridges of crystalline rock, in most 

 places so imperfectly exposed that their subdivisions can scarcely be 

 made out, and that geologists may even be excused for doubting the 

 stratified character of their rocks. It is only by comparing them 

 with the magnificent series exposed in the country north of the St 

 Lawrence, and worked out so ably by Logan, that the more limited 

 exposures of the Atlantic margins can be understood. 



In the Journal of the Geological Society for February 1865 will be 

 found a summary statement by Logan of the structure of this formation, 

 which still holds good.J He there divides the Laurentian into two 

 series, the lower and the upper, the former largely composed of ortho- 

 clase-gneiss, but Avith beds of limestone, quartzite, the micaceous and 

 hornblendic schists in its upper parts ; the latter composed of similar 

 gneisses and limestones, but with beds of gneissose anorthosite and 

 labradorite, and great masses of coarsely cleavable labradorite and 

 hypersthene. 



It is perhaps unfortunate that these last masses, many of them, no 

 doubt, accidental and intrusive, so forcibly attracted the attention of 

 Logan that he characterized the Upper Laurentian as a labradorite 



* See, however, Winchell Minnesota Reports, 1884-88. 

 t Matthew, Canadian Record of Science, 1887. 

 t "On the Eozoic and Paleozoic Rocks." 



