584 UPPER AND LOWER LAURENTIAN. [Ch. XXVII. 



stone and the other " primordial " rocks were formed. The older 

 half of this Laurentian series is unconformable to the newer portion 

 of the same. 



Upper Laurentian or Labrador Series. — The Upper Group, more 

 than 10,000 feet thick, consists of stratified crystalline rocks in which 

 no organic remains have yet been found. They consist in great part 

 of felspars, which vary in composition from anorthite to andesine, or 

 from those kinds in which there is less than one per cent, of potash 

 and soda to those in which there is more than seven per cent, of these 

 alkalies, the soda preponderating greatly. These felsparites sometimes 

 form mountain masses almost without any admixture of other minerals ; 

 but at other times they include pyroxene, which passes into hyper- 

 sthene. They are often granitoid in structure. One of the varieties 

 is the same as the opalescent labradorite rock of Labrador. The Adi- 

 rondack Mountains in the State of New York are referred to the same 

 series, and it is conjectured that the hypersthene rocks of Skye, which 

 resemble this formation in mineral character, maybe of the same geo- 

 logical age. 



Lower Laurentian. — This series, about 20,000 feet in thickness, is, 

 as before stated, unconformable to that last mentioned ; it consists in 

 great part of gneiss of a reddish tint with orthoclase felspar. Beds of 

 nearly pure quartz, from 400 to 600 feet thick, occur in some places. 

 Hornblendic and micaceous schists are often interstratified, and beds 

 of limestone usually crystalline. 



There are several of these limestones which have been traced to 

 great distances, and one of them is from 700 to 1500 feet thick. In 

 the most massive of them Sir W. Logan observed in 1859 what he 

 considered to be an organic body much resembling the Silurian fossil 

 called Stromatopora rugosa. It had been obtained the year before by 

 Mr. J. McCulloch at the Grand Calumet on the river Ottawa. This 

 fossil was examined in 1864 by Dr. Dawson of Montreal, who detected 

 in it, by aid of the microscope, the distinct structure of a Rhizopod or 

 Foraminifer. Dr. Carpenter and Prof. T. Rupert Jones have since 

 confirmed this opinion, comparing the structure to that of the well- 

 known nummulite. It appears to have grown one layer over another, 

 and to have formed reefs of limestone as do the living coral-building 

 polyp animals. Parts of the original skeleton, consisting of carbonate 

 of lime, are still preserved ; while certain interspaces in the calcareous 

 fossil have been filled up with serpentine and white augite. On this 

 oldest of known organic remains Dr. Dawson has conferred the name 

 of Eozoon Canadense ; its antiquity is such that the distance of time 

 which separated it from the Upper Cambrian period, or that of the 

 Potsdam sandstone, may, says Sir W. Logan, be equal to the time 

 which elapsed between the Potsdam sandstone and the nummulitic 

 limestones of the Tertiary period. The Laurentian and Huronian 

 rocks united are about 50,000 feet in thickness, and the Lower Lauren- 

 tian was disturbed before the newer series was deposited. We may 



