LAUltENTlAN AND HUHONIAN. 47 



as Laiirentinn, in Bohemia large areas have been so recognized hy Bar- 

 rande, and in Norway and Sweden the crystalline rocks bearing th(! iron 

 ores have also been referred to the same age. 



In Canada the Laurentian is subdivided inti) Lower and Upper, and 

 the two groups are supposed by Sir William Logan to be separated by 

 unconformity and by a long interval of time. The upper and less im- 

 portant group is especially characterized by the abundance of the oi)alescent 

 labradorite feldspar, and is particularly well developed in Labrador. It has 

 been called by Dr. Hunt the Norian or Labradorian series, and it has been 

 recognized by him in the Adirondack region and elsewhere in the eastern 

 United States, though it is not yet known to be a persistent member of the 

 Eozoic of the Appalachian Mountains. 



The Huronian system was first studied on the Canadian border of 

 Lake Huron, where its rocks are typically developed and are found to 

 overlie unconformably rocks of well known Laurentian age. They are as 

 a rule here more silicious in their character than the Laurentian, and con- 

 sist chieflv of silicious slates and conglomerates, quartzite, jasper, diorile, 

 and chloriti(; and epidotic rocks, with ores of iron. The Huronian is less 

 widely recognizable and distinguishable than the Laurentian, and where its 

 occurrence is maintained beyond the region of its typical development, the 

 opinion rests solely upon lithological characters. 



The iron-bearing region on the south shore of Lake Superior is in part 

 regaded as of Laurentian age, but the iron-bearing strata of the Marquette 

 region are very generally considered to be Huronian. On our eastern coast 

 the existence of the Huronian is announced as probable. Credner refers 

 to this age a series of rocks in the Appalachian Mountains from the Saint 

 Lawrence to Georgia, which includes most of the auriferous rocks of that 

 region. Hunt also, who has devoted much time and study to the exami- 

 nation of the Eozoic rocks of Canada and the northern part of the Appa- 

 lachian Mountains, regards a portion at least of the Green Mountain series 

 of Vermont as of Huronian age, and believes that they may be traced 

 southwestward through Pennsylvania to Virginia. In the Green Mountain 

 series the rocks are gneisses (more micaceous than the Laurentian), diorites, 



