2IO STRATIGRAPIIICAL GEOLOGY. 



geology of Canada for 1863 * great vertical thicknesses of the Laiirentian 

 gneiss are distinguished mineralogically from the others by the presence 

 of triclinic feldspars, and the rocks termed anortJiosites. I understand 

 that there are scarcely any orthoclase gneisses interstratified with the 

 anorthosites. Later in the same volume certain facts are stated, render- 

 ing it probable that the anorthosite series unconformably overlies the 

 gneiss having beds of limestone in it.f The formal proposal of this sub- 

 division is presented in the atlas accompanying this report, issued in 1865, 

 where the anorthosite group is distinguished as the Upper Lmirentian or 

 Labrador series, and the other the Lower Laurentian. The nomencla- 

 ture of this atlas is based upon further exploration. Had this not been 

 satisfactory, the distinction would certainly not have been delineated in 

 the atlas. The evidences of unconformity consist in the concealment of 

 beds of limestone by the upper rocks covering them, and the change of 

 strike. The testimony of Mr. James Richardson, to the relations of the 

 Lower and Upper Laurentian on the north shore of the St. Lawrence, in 

 1869, confirms the reality of the division. He represents the dip of the 

 Laurentian to be nearly vertical, with a north and south strike, while the 

 labradorite rocks dip at comparatively moderate angles, with a strike 

 nearly east and west.^ Seven areas of labradorite rocks outside of New 

 England are represented upon Plate I of this volume, — five north of the 

 River St. Lawrence, one in Newfoundland, and one in New York. It is 

 spoken of as occurring in Alabama, in the recent report of Dr. Eugene 

 A. Smith, and much of the mineral occurs at other localities along the 

 Atlantic range, as in North Carolina and Pennsylvania. None of the 

 Labrador areas, whether in America or Europe, have yet been carefully 

 studied stratigraphically, so that we have not the means of knowing their 

 thickness. The lines of iron ore and other foreign minerals better agree 

 with the idea of stratification than to suppose the masses are eruptive. 

 In the study of New England rocks, the labradorite aids us greatly, since 

 most geologists are prepared to accept it as indicating formations of 

 Eozoic date; and, if these triclinic feldspar layers rest upon strata for- 

 merly thought to be Paleozoic, they render it probable that both the un- 

 derlying and contiguous masses belong to very ancient systems. 



* Ceol. Survey of Canada, Report for 1863, pp. 22, 23, 478, and 586. \Id., p. 839, 

 Xld., Report 1866-69, p. 306. 



