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



not sheet-like, but tend rather to occur as large, irregular 

 masses or bunches, from which short and long stringers run 

 out in all directions. The shapeless type is particularly char- 

 acteristic of those veins which are in the pelitic and graphitic 

 rocks, while the sheet forms are found chiefly in the psammites 

 and psephites, where they occupy joint-fissures. It is im- 

 portant to note not only that a great majority of these veins 

 are in rocks of fine texture, but also that they are especially 

 abundant where the country rock is much contorted. Local- 

 ities where quartz veins are numerous and where contortion in 

 the schists is at a maximum are as follows : southern end of 

 Warwick Neck (D : 7) ; part of the coast of Bristol Neck, 

 northwest of Bristol (GT : 5-6) ; Brayton Point (Loc. 49, J : 5) ; 

 several places along the eastern coast of Aquidneck Island ; 

 along the eastern shore of the Sakonnet River, north of Brown 

 Point (Loc. 44, 1 : 12) ; Sachuest Neck ; Gould Island (E : 12) ; 

 numerous points on the eastern coast of northern Conanicut 

 Island ; on Freebody's Hill (between Locs. 17 and 19, D : 13) 

 and on the Beaver Tail Peninsula (Loc. 23, D : 14 and 15), 

 Conanicut Island ; Dutch Island (Loc. 14, C-D : 13) ; and at 

 points along the western coast of the Bay. Whether introduc- 

 tion of the veins was consequent upon the intense folding, or 

 vice versa, is a question to be discussed later. 



As with the pegmatite apophyses on the Bonnet, the state- 

 ment holds here also that veins which cross the schistosity are 

 generally thicker and more contorted than those which run 

 nearly parallel to it. Except in this way, the veins exhibit 

 very little dependence upon directional structures of the coun- 

 try rock. 



The edges of the veins, always sharply outlined, are ordin- 

 arily uneven or jagged. Horses of the country rock are not 

 infrequent. Exomorphic change is seen in an excess of 

 sericite, oriented parallel to the contact as if caused by pressure 

 concentrated near the vein. 



The presence of feldspar along the margins, as already 

 described for certain cases, might be attributed to the action of 

 the injected material upon a country rock containing the 

 elements of this feldspar ; but the fact that the relative propor- 

 tion of this mineral (1) does not vary sympathetically with dif- 

 ferences in the composition of the surrounding rock, and (2), 

 when studied at different localities and compared, reveals a 

 general and uniform increase in a southwesterly direction, 

 toward the pegmatites and the granite, discountenances such 

 an assumption. 



Summary. — We may now summarize the points brought 

 out in describing the Acid Intrusive Series, at the same time 

 applying the facts noted under the theoretical considerations. 



