DESCRIPTION'S OF THE FORMATIONS. 11 



In the Atlantic belt, considerable areas of Laurentian occur in Newfoundland, 

 and probably in several parts of New England. A range of Laurentian rocks from 

 the western part of Connecticut extends south westward, forming the Highlands of 

 the Hudson, and making the South Mountain as far as the Schuylkill ; while a 

 smaller range of the same, to the southeastward, forms the Welsh Mountain, in 

 Pennsylvania. Little is known of the distribution of the Laurentian farther 

 southward along the Atlantic belt, but the gneisses near Richmond in Virginia, and 

 those of Roan Mountain, in North Carolina, are referred to this terrane. 



Large areas of Laurentian occur around Lake Superior, and farther west in the 

 Rocky Mountains, where they form the crystalline rocks of the Colorado range in 

 the east, and the Wahsatch in the west, and probably occur in many other parts 

 of the region. To the Laurentian belong the gneisses of the "Western Islands of 

 Scotland, those of Scandinavia and Finland, and large portions of those of the 

 Alps. The limestones of the Laurentian contain the remains of a foraminiferal 

 organism known as Eozoon Canadense, (Dawson) which has been found hi several 

 localities in Canada, and also in Bavaria, and in Finland. Accompanying it are 

 several other small forms, regarded as organic, and referred to the protozoa. 



1 b, Norian, The upper portion of the Laurentian series on the Ottawa 

 river, was originally defined by the geological survey of Canada as consisting of a 

 rock, gnessoid or granitoid in character, made up chiefly of labradorite, or related 

 anorthic feldspars, but including also true gneisses and crystalline limestones, not 

 unlike those already described hi the Laurentian. Subsequent studies hi Canada 

 led to the conclusion that these rocks constitute a distinct terrane, resting 

 unconforrnably upon the gneisses and crystalline limestones of the preceding 

 series, and the two were respectively designated as Lower Laurentian, and Upper 

 Laurentian or Labradorian. As the newer is very distinct from the older terrane, 

 it has, however, been thought better to restrict the name of Laurentian to the 

 latter. A series precisely similar to the upper one occurs in Norway, where, as in 

 North America, it rests upon Laurentian gneisses, and where the name of norite 

 has been given to the f eldspathic rock which is its chief characteristic. Hence the 

 name of Norian, which has been chosen, in place of Upper Laurentian, as the 

 designation of the terrane. It is conjectured, from, the fact that it has yet been 

 found only in contact with the Laurentian, and from its including gneisses and 

 limestones lithologically similar to those of the latter, that it is next in age. 



The norites consist, for the greater part, of anorthic feldspar, sometimes 

 almost without admixture, but at other times accompanied by small portions of 

 hornblende, of pyroxene or of hypersthene, constituting what has been called 

 hypersthenite or hyperite. Red garnet, green epidote, biotite, and ilmenite are 

 often present, and all of these minerals are generally arranged in such a way as to 

 give a gneissoid structure to the rock. The texture is sometimes fine-grained and 

 compact* and at other times more coarsely granular, and even granitoid, displaying 

 great masses of anorthic feldspar, frequently opalescent, and varying in composition 

 from auorthite to andesin'e. The colors of the norites vary from white, pale 

 bluish or greenish to dark lavender or smoke-blue, or nearly black The characters 

 of the associated gneisses and limestones, as already remarked, are similar to those 

 of the Laurentian. Great beds of highly titaniferous iron ore abound in the 

 Norian series. 



