WARREN AND PAL.\CUE. — QULNCY PEGMATITES. 139 



first the dark margiual band (Zone A, Figure 2) here wider than fur- 

 ther south, less sharply defined, coarser, and at the lower end merging 

 almost imperceptibly into the surrounding granite. 



As in the previous section this zone is succeeded by graphic-granite 

 and uneven though rather coarse granite or pegmatite forming together 

 a zone about 2 feet in width in its eastern and thickest portion, but 

 much narrower on the western side as shown in the figure (B, Figure 2). 

 It will be noted that in the figure a continuous band of graphic-granite 

 (crossed) has been indicated just inside the dark margin ; also another 

 strip within the zone running parallel to the boundary. This misrep- 

 resents the actual facts to some extent. The graphic-granite is not, 

 so near as could be told, entirely continuous, but is replaced at times, 

 either by the coarse pegmatite, or by a finer, granular rock carrying 

 rounded quartz grains and relatively long, slender riebeckite crystals. 

 Occasionally streaks of large feldspar crystals lie in this latter material 

 with an arrangement rudely parallel to the margins of the zone. These 

 variations seemed particularly strong on the western side of the pipe, 

 but the exact extent, however, of the graphic-granite, etc., was exceed- 

 ingly difficult to trace accurately and no attempt to do so has been 

 made in the figure. As elsewhere, the gradation of the graphic-granite 

 into the main rock of the pipe is almost imperceptible. The texture 

 and mineral composition of the main part of this zone is practically 

 identical with that of zone B of Figure 1, previously described. 



Along a somewhat irregular surface this zone changes rather abruptly 

 both as to texture and mineral composition into the next zone (C of 

 Figure 2). This latter varies considerably in thickness and consists of 

 numerous, relatively large, rudely rectangular crystals of microcline 

 (range of size, 4 or 5 mm. by 2 or 3 cm.) with xenomorphic borders, 

 embedded in a groundmass consisting essentially of microcline and 

 aegirite, quite fine in grain and highly porous in texture. In this 

 groundmass the microcline usually predominates in amount although 

 frequently the aegirite equals or exceeds it. Quartz, while present in 

 the form of small grains in the groundmass, is hardly more than an 

 accessory. As the walls of the central pocket are approached this 

 rock becomes essentially a mass of rather loosely cohering, white or 

 cream-colored microcline crystals and very abundant, dark green to 

 almost black aegirite prisms and needles, the whole filled with small 

 ramifying pockets into which the free ends of the crystals project. 

 Although much of this material is rather course (centimeter) grained 

 there is also a large amount of fine material. The feldspar crystals, 

 although somewhat kaolinized in ])laces, are as a whole remarkably 

 fre.sh. Some crystals are deeply pitted by solvent action and where 



