161 



and gneiss are not found in Methuen or beyond ; and the faults 

 probably unite in one, or pei'haps die out, there. North-east 

 of Dracut the synclinal is certainly known to contain only 

 mica slate ; but indications are not wholly wanting of the ex- 

 istence in the axis of the synclinal of conglomerate and, 

 possibly, argillite. This part of the State has a thick covering 

 of drift and outcrops are few, but Mr. C. W. Kempton has ob- 

 served a distinct conglomerate, apparently in situ, in Haverhill, 

 about midway between the Merrimac and the State line. This 

 conglomerate appears to be identical or nearly so with that in 

 Harvard ; and, since the latter is intimately associated with 

 argillite, I should not be surprised to hear of the discovery of 

 argillite in the valley of the Merrimac. In fact it is well known 

 that much of the so-called mica slate in this basin is more 

 argillaceous than micaceous. 



The striking parallelism of the principal faults of the 

 Montalban system with those of the Huronian suggests their 

 synchronism ; and this view is strengthened by the probability 

 already pointed out that some of these great dislocations trav- 

 erse the strata of both systems. 



GENERAL RELATIONS OF THE OLDER CRYSTALLINE FORMA- 

 TIONS OF EASTERN MASSACHUSETTS. 



The oldest and most thoroughly crystalline rocks in Massa- 

 chusetts, so far as known, are those composing the Naugus Head 

 series. This series, in its normal position, underlies all else in 

 this region ; and reposing directly upon this most ancient forma- 

 tion we have the Huronian system, — granites first and diorites 

 last. The Huronian granites are to a large extent exotic, and 

 hence are out of their normal or original position with relation 

 to the other members of the system ; but this is believed not to 

 be the case with the large area in southern Norfolk and northern 

 Plymouth and Bristol Counties, viewed as a whole. This im- 

 mense mass of granite is the centre or axis of our Huronian 

 series ; the strata become newer as we recede from it north- 

 westerly ; and the probable existence of petrosilex on its 



OCCAS. PAPERS B. S. N. H. — IH. 11 



