No. 1.] " SELWYN — THE QUEBEC GROUP. 27 



several areas where they are known to occur in Canada, have 

 they yet been mapped in detail, and even their limits, as indica- 

 ted on the geological map, are more or less conjectural. This 

 appears to be likewise the case as regards the areas where they 

 have been noticed in Essex and adjoining counties in New York 

 State and in New Hampshire, where Profess^ir Hitchcock shews 

 that they rest unconformably on the upturned edges of the " Mont- 

 alban " gneisses,^ leading to the conclusion that the gneisses of 

 the White Mountains are older than the *'Norian," whereas 

 Dr. Hunt, solely, I believe, on mineralogical considerations, sup- 

 poses these same '■'• Montalhan'''' gneisses to constitute a system 

 newer than the Huronian. Here then, as in the Hastings region, 

 we find theory and experience at variance. But the question 

 suggests itself, may we not have labradorite rocks belonging to 

 systems younger than Laurentian ? Dr. Hunt refers (§ 318), 

 to the valuable chemical and microscopic examination of these 

 rocks in Essex county, New York, by Mr. Albert Leeds, the 

 results of which are given in the American Chemist, March, 

 1877 ; but Mr. Leeds does not appear to have studied the 

 stratigraphy of the region, and his general conclusions are stated 

 as follows : 



" That these norites are a stratified rock but have undergone 

 a metamorphosis so profound as to have caused them to be re- 

 garded by Emmons and earlier observers as unstratified. The 

 dolerites which are formed of the same constituent minerals, 

 and are of the mean specific gravity of these norites, have prob- 

 ably been formed from a portion of these stratified deposits, by 

 deeply seated metamorphic action and have further modified and 

 greatly tilted the superposed rocks in the course of their extru- 

 sion." 



Prof. James Hall in 1866f has stated his conclusions that the 

 limestones of Essex and adjoining counties in New York State 

 " do not belong to the Laurentian system either lower or upper." 

 The facts, on which a part of this conclusion is based, viz. the 

 unconformity of the Laurentian limestone series to the lower 

 orthoclase gneisses agree with those of Mr. Vennor, and there 

 is, I think, but little doubt that all these crystalline limestone 

 groups — that is those of Essex and St. Lawrence Counties, U. S. 



* Geology of New Hampshire, Vol. II, pp. 217-218. 

 t A. J. of S. Vol. XII, p. 298. 



