III.] THE CHEMISTRY OF METAMORPHIC ROCKS. 29 



I. The Laurentian system represents the oldest known rocks 

 of the globe, and is supposed to be the equivalent of the Primi- 

 tive Gneiss formation of Scandinavia, and that of the Western 

 Islands of Scotland, to which also the name of Laurentian is 

 now applied. It has been investigated in Canada along a 

 continuous outcrop from the coast of Labrador to Lake Su- 

 perior, and also over a considerable area in northern New 

 York. 



II. Associated with this system is a series of strata charac- 

 terized by a great development of anortholites, of which the 

 hypersthenite or opalescent feldspar-rock of Labrador may be 

 taken as a type. These strata overlie the Laurentian gneiss, 

 and are regarded as constituting a second and more recent 

 group of crystalline rocks, to which the name of the Labrador 

 series may be provisionally given. [Since called dorian ; 

 see note to page 31.] From evidence recently obtained, Sir 

 William Logan conceives it probable that this series is uncom- 

 formable with the older Laurentian system, and is separated 

 from it by a long interval of time. 



III. In the third place is a great series of crystalline schists 

 (the Green Mountain series), which are in Canada referred to 

 the Quebec group, an inferior part of the Lower Silurian sys- 

 tem. They appear to correspond both lithologically and strati- 

 graphically with the Schistose group of the Primitive Slate 

 formation of Norway, as recognized by Naumann and Keilhau, 

 and to be there represented by the strata in the vicinity of 

 Drontheim, and those of the Dofrefeld. The Huronian series 

 of Canada in like manner appears to correspond to the Quart- 

 zose group of the same Primitive Slate formation.* It consists 

 of quartzites, varieties of imperfect gneiss, diorites, silicious 

 and feldspathic schists passing into argillites, with limestones, 



and great beds of hematite The Huronian series is as 



yet but imperfectly studied, and for the present will not be 

 further considered, t 



* See Macfarlane, Primitive Formations of Norway and Canada com- 

 pared, Canadian Naturalist, VII. 113, 162. 

 [ t It will be seen above that I have indicated. Jive groups of crystalline rocks, 



