UPPER AND LOWER LAURENTIAN. 
491 
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 feldspars, which vary in compo¬ 
sition 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 al¬ 
kalies, the soda preponderating greatly. These feldsparites 
sometimes form mountain masses almost without any admix¬ 
ture of other minerals; but at other times they include ,au- 
gite, which passes into hypersthene. They are often granit¬ 
oid in structure. One of the varieties is the same as the 
opalescent labradorite rock of Labrador. The Adirondack 
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, 
may be of the same geological age. 
Lower Laurentian. —This series, about 20,000 feet in 
thickness, is, as before stated, unconformable to that last 
mentioned; it consists jn great part of gneiss of a reddish 
tint with orthoclase feldspar. Beds of nearly pure quartz, 
from 400 to 600 feet thick, occur in some places. Horn- 
blendic and micaceous schists are often interstratified, and 
beds of limestone, usually crystalline. Beds of plumbago 
also occur. That this pure carbon may have been of or¬ 
ganic origin before metamorphism has naturally been con¬ 
jectured. 
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 ru- 
gosa. It had been obtained the year before by Mr. J. Mac- 
Mullen at the Grand Calumet, on the river Ottawa. This 
fossil w^as examined in 1864 by Dr. Dawson of Montreal, who 
detected in it, by aid of the microscope, the distinct struc¬ 
ture of a Rhizopod or Foraminifer. Dr. Carpenter and Prof. 
T. Rupert Jones have since confirmed this opinion, compar¬ 
ing 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 inter¬ 
spaces in the calcareous fossil have been filled up with serpen¬ 
tine and white augite. On this oldest of known organic re¬ 
mains Dr. Dawson has conferred the name of Eozoon Cana- 
