F. H. Lahee — Metamorphism and Geological Structure. 449 



joint planes or along the cleavage of the southern Conanicut 

 Carboniferous schists. Or, again, the dikes may cut indis- 

 criminately across such structures. In most cases their thick- 

 ness is rather variable. Short apophyses may pass from them 

 into the country rock, and small inclusions of the latter maybe 

 seen. Exomorphically the schists have been somewhat baked 

 and bleached. The most obvious endomorphic features are 

 the decrease in size of grain toward the contact and the par- 

 allelism of the biotite flakes with the walls (flow structure), as 

 noted by Collie* and Pirsson.f Locally these dikes show some 

 folding and schistosity. Yeins of massive, milky quartz, some- 

 times of considerable size, intersect them with sharp contacts. 



From these petrographic and structural relations, it would 

 seem that the minette dikes were injected into the Carbonifer- 

 ous sediments before the period of deformation came to an end, 

 yet after schistosity and jointing had been developed in the 

 country rock4 



— Summary. — Dikes of minette (a) have been found in a few 

 places in the southern part of Conanicut Island ; (b) are clearly 

 intrusive into, and are, therefore, later than, the Carboniferous 

 sediments and the pre-Carboniferous Conanicut granite ; (c) 

 were injected during the general period of deformation of the 

 Carboniferous series ; (a) are themselves cut by numerous 

 veins of massive, milky quartz. 



Acid Intrusives. 



Introductory remarks. — We have already mentioned the 

 fact that the granitic rocks in South Kingstown are probably 

 intrusive into the Carboniferous sediments, and that they are 

 not pre-Carboniferous as had formerly been supposed. Since 

 these granites — part of the Sterling series — are especially 

 prominent on Boston Neck (B : 14 and 15, fig. 1), they may be 

 referred to as the ' Boston Neck granite.' They appear to be 

 closely related in origin to the great group of pegmatites and 

 quartz veins which likewise cut the Carboniferous rocks. 

 Herein we shall denote the Boston Neck granite, the pegma- 

 tites, and the associated quartz veins by the general term, 

 i Acid Intrusive Series.'§ 



*Op. cit., p. 228. fOp. cit. 



^Pirsson (op. cit., pp. 371-372) said that the schistosity, folding, and 

 faulting in the dikes were caused by dynamic forces acting along north-south 

 lines after intrusion. Collie (op. cit., pp. 228-230) stated that the nearly 

 north-south dikes are schistose because they lie nearly at right angles to the 

 direction of the forces ; the east-west ones are folded and faulted. 



§ Dr. Loughlin, in his ' Intrusive Granites and Associated Metamorphic 

 Sediments in Southwestern E. I.' (this Journal, xxix, 447, 1910), presents 

 evidences for the genetic relationship of the granites of southwestern Rhode 

 Island, the pegmatites, and the quartz veins. From investigations carried 

 on in the extreme eastern portion of Dr. Loughlin's area and eastward, pre- 

 vious to the publication of the paper just cited, the writer had arrived at 

 similar conclusions, and, certainly in that region where the fields of work 

 overlap, he is in agreement with Dr. Loughlin. 



