On the Norian or "Upper Laurentian" Formation. 425 



of their chemical composition. Four analyses made by 

 him are noted on page 436. 



If we add to these works a short essay by Hall, 1 we 

 have all that has been published up to date on this area, 

 which certainly deserves a more careful study. 2 The pre- 

 cise relations of these anorthosites to the surrounding 

 gneiss are not yet known. Emmons says they gradually 

 pass into one another, whereas Hall maintains that the 

 anorthosites lie unconformable on the gneiss. He goes 

 even so far as to pronounce the crystalline limestone 

 which occurs with the gneiss to be a distinct series uncon- 

 formably overlying the gneiss and the anorthosite. All 

 the other geologists have considered these here as in Canada 

 to be members of the Laurentian. These conclusions 

 were, moreover, drawn by him without making an accu- 

 rate geological investigation of the whole district, which- 

 alone, in such a series of folded rocks, would render it 

 possible to form an accurate opinion. Such an investi- 

 gation would in all probability show that the anorthosite 

 here cuts through the gneiss as it does in Canada. 



The rock is sometimes massive, sometimes indistinctly 

 streaked or foliated, showing sometimes very clearly the 

 peculiar brecciated structure which was described in the 

 rocks of Morin and of the Saguenay, where fragments, 

 often of considerable size, of the dark coloured and fre- 

 quently opalescent plagioclase are imbedded in a lighter 

 coloured mass of the same mineral. Here likewise the 

 plagioclase predominates, the rock consisting often entirely 

 of this mineral. Hypersthene, diallage, hornblende, biotite, 

 garnet and iron ore sometimes occur along with the pla- 

 gioclase. Epidote and prehnite were found as secondary 

 i 



i Hall, Xote on the Geological Position of the Serpentine Limestone of Northern 

 New York, etc.— Am. Jour. Sc., July, 1876. 



2 Note.— Since the publication of the present. paper, in 1893, several important con- 

 tributions to our knowledge of this district have appeared by J. F. Kemp, C. H. Smyth, 

 Jr., and C. R. Van Hise. See list of papers on page 442. 



