GEOLOGICAL RELATIONS. 9 



Laurentiaii. Beginning at the south-west corner, we observe three 

 areas marked as of this age. Tlie greater one comprises the liighlands 

 of New York and New Jersey. Nearly all writers have agreed in this 

 reference, save that Prof. H. D. Rogers at one time regarded the crys- 

 talline limestones of New Jersey as metamorphosed Lower Silurian. Prof. 

 W. W. Mather separated from this "Primary" area various metamorphic 

 limestones and schists, thought to be of Silurian age, which are mostly 

 placed with the Atlantic system upon our map. Hall and Logan, in 1864, 

 found this so-called primary area in eastern New York to be the same 

 with what they had elsewhere called Laurentian.* Prof. Dana comes to 

 a similar conclusion.! 



The two smaller areas to the north-east, partly in Connecticut and 

 Massachusetts, are Formations K 2 and K 3 of Percival, and are accepted 

 as Laurentian by Profs. Hall and Dana. The correctness of the bounds 

 of the latter area in Massachusetts may be open to question. 



The large areas of Laurentian, in the Adirondacks and north of the St, 

 Lawrence river in Canada, are the exposures originally called by this 

 appellation by Sir W. E. Logan. 



In New Brunswick this formation has been outlined in accordance 

 with the views of Bailey and Matthews. 



In Nova Scotia, the metamorphic rocks accompanying the magnetic 

 iron ores of the Cobequid mountains and an extensive area running the 

 whole length of the peninsula, are referred to this period by Hugh 

 Fletcher, of the geological survey of Canada, in the topographical atlas 

 of the Dominion of Canada (1875), published with the approval of Mr. 

 Selwyn, the director of the survey. In accordance with the views of T. 

 Sterry Hunt, the latter area is placed in the Atlantic group. 



The more central portions of Newfoundland, embracing more than half 

 its territory, may be referred to the Laurentian. 



PorpJiyritic gneiss and undetermined granites. The importance of this 

 group in New Hampshire has been set forth to some extent in the first 

 volume. Upon the authority of the text of the Massachusetts report, 

 I have added an area between Worcester and the Connecticut valley. 

 There is probably another in Warwick. I cannot satisfy myself from 

 Percival's report that this formation occurs in Connecticut. The one 



* Amer. Jour. Sci., II, vol. xxxix, p. 96. f I^i- HI. vol. iii, p. 255. 

 VOL. II. 2 



