440 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



no evidence in support of this view. (Araer. Jour. Sci., 1883, (3) XXY., 



pp. 65-71.) 



Dr. Wads worth showed, in 1881, that the Quincy granite was intru- 

 sive in the fossiliferous argiUite, and that the supposed sandstone and 

 quart^ite of Professor Shaler — the felsitc (orthophyre) of Dr. Hunt — 

 was simply the granite modified by its contact with the argillito. No 

 faulting existed, for the two rocks were welded into a solid mass. lie 

 also pointed out that the dip of the argillito was southerly, instead of 

 northerly,, as had been claimed by Messrs, Rogers, Jackson, and Shaler. 

 (Proc. Eost. Soc. Nat. Hist, 1881, XXL, pp. 274-277.) 



VERMONT AND WESTERN MASSACHUSETTS. 



The geology of Eastern Massachusetts presents us, as has been seen 

 in the preceding pages, with a complication of problems, toward tlic 

 solution of which but little progress was made by the earlier investiga- 

 tors. A similar condition of things is revealed when we examine what 

 has been published in regard to the age and sequence of the formations 

 in the western portion of the State. Of what was known on this sub- 

 ject at the time of the publication of President Hitchcock's Final Re- 

 port on the Geology of Massachusetts (18fl), a good idea may be formed 

 from the following quotation from that work in regard to the age of the 

 limestone of Berkshire County : 



" According to the views which have now been suggested, it will follow, that 

 wherever we find the limestone of Berkshire county enclosed between strata 

 of gneiss, it must be regarded as the oldest variety of that rock, or primary 

 limestone. Where it is inters tra Lifted with mica and talcose slate, although 

 more recent than in gneiss, it ought still probably to be regarded as primary. 

 But when we find it above these rocks ; . . . . then as it hes mnnediately 

 beneath clay slate, it may be what i« called primary, or what is called transi- 

 tion, according as we place clay slate on the one class or the other." (Fnial 

 Report on the Geology of Massachusetts, p. 581.) 



Prof. H. D. Rogers, in 1856, in his sketch of the geology of the 

 United States, furnished for publication in Johnston^s Physical Atlas, 

 makes two periods below the " Cambrian or Older Silurian "; one, the 

 " Azoic or Scmi-Metamorphic " ; the other, the " Hypozoic, or True 

 Metamorphic." The basis on which this classification rests seems to be 



