13 



EOZOIC FORMATIONS. 



The oldest of these crystalline series is the smallest in extent.- 

 I propose to designate it, provisionally, as the Naugus Head 

 series , — in allusion to the promontory of this name on 

 the Marblehead shore, where the rocks of this series are best 

 develo]j)ed and were first observed. Succeeding the Naugus 

 Head series, in the order stated, are the Huronian and Montal- 

 ban systems, and a series of semi-crystalline rocks, of very 

 dissimilar composition, but appearing to be identical in age and 

 geognostic relations, which, having their greatest development 

 in the vicinity of Boston, I have named collectively the Shaw- 

 mut group , — Shawmut being the ancient Indian name of 

 Boston. 



In employing the names "Huronian," " Montalban," etc., 

 terms having chronological signification, to designate the crys- 

 talline divisions of Eastern Massachusetts, I mean to assert 

 the general lithological and stratigraphical resemblance, but 

 not necessarily the chronological equivalence, of the groups 

 thus designated to the great and generally recognized Eozoic 

 divisions of other regions. My views on this subject cannot 

 be justly characterized as merely speculative ; for at all impor- 

 tant points they rest on the solid ground of facts. My position 

 with respect to our crystalline or Eozoic formations, briefly 

 stated, is this : There exists in Eastern Massachusetts a great 

 series of crystalline schists agreeing in all important respects 

 with the Montalban system as defined by Dr. T. Sterry Hunt. 

 Farther east is another vast crystalline formation, differing 

 widely from the first, and possessing all the essential char- 

 acters of the Huronian. This second series is plainly older 

 than, and underlies, the first ; and it is underlaid in its turn by 

 a still more ancient-looking terrane which, consisting prin- 

 cipally of coarsely crystalline, and frequently exotic, basic 

 rocks, presents a general resemblance to the Upper Laurentian 

 or Norian series of the Canadian geologists. This, as above 



