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BULLETIN OF THE 



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ever, is not in the line of strike of tlic. main, or westerly part of the dike, 

 but lies some hundred feet to thj north. Whether this ehange is due to 

 a horizontal throw^ or to a fresh outbreak of dike along a parallel line, 

 does not appear. 



At the western end, on the southern side, the jnnetion with the con- 

 glomerate and red sandstone is very irregular, — large and small tongues 

 of the dike penetrate into the conglomerate, this rock having a strike 

 N. 60°-80° W., and a dip 70° south. The jmiction between the two 

 rocks is sharp and well marked : the dike seems often amygdaloidal near 

 the junction. Sections of the contact of the two rocks show that the dike 

 is composed of a mass of very small feldspars, having a beautiful fkiidal 

 arrangement, while they are often bent when in contact with the line of 

 the conglomerate. On the northern side, a fine vertical exposure of the 

 junction is obtained, which is seen to stand almost vertical ■ the dike 

 cutting the slate and conglomerate a little irrcgularl}^, but standing 

 nearly parallel to the stratification. The conglomerate hero is nearly 

 vertical, but may be said to dip to the north very steeply; if, however, 

 v/e pass east along the strike, a few hundred yards, to the exposures in 

 the field, we find that all the conglomerate, both north and south of the 

 line of the dike, dips steeply in one direction, i. e. south. I cannot, 

 therefore, agree with Mr. Crosby, that " this is clearly a faulted anticlinal 

 fold." It may equally well be an intrusion of the dilic into the verti- 

 cally standing strata, causing irregularities of the dip. More detailed 

 study is required. In the western ridge the dike has a width of about 

 three hundred feet from contact to contact. 



The rock is generally of a greenish color, approaching a greenish red 

 in the fresher portions ; it is irregularly jointed. In texture there is 

 great variation between coarse, fine, porphyritic, and amygdaloidal. 

 Masses of quartz, and yellowish-green epidotic material frequently occur. 

 These greenish masses are often very irregular, occasionally vertically 

 banded, and resembling fragments of a stratified rock, and often lined on 

 the exterior with a band of reddish substance. Microscopic sections of 

 some of them give a mixture of quartz, calcite, cpidote, and a whitish 

 opaque substance (kaolin 1), and show that they are in part areas in the 

 rock of decomposition, or segregation. 



Although at first sight this dike appears to be a homogeneous mass of 

 rock, yet it is in reality composed of rocks belonging (in all probability) 

 to at least three separate eruptions, forming, instead of one, numerous 

 dikes. To this fact is largely due the noticeable variations in the area 

 of rock. First in order comes the amygdaloid, forming the principal 



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