13G PROCEEDINGS OF THE AMERICAN ACADEMY. 



pear at least in thin section to lack sharp crystalline form. The larger 

 grains commonly show a fine zonal structure ; the small ones are 

 usually clustered, sometimes with parallel orientation and sometimes 

 without, but in the latter case forming a mass often suggesting a 

 larger crystal in outline as in the Ballou pegmatite. The zircon 

 also lies almost wholly in the quartz or between it and the feldspar. 

 Only a few grains have been noted in the microcline. Ilmenite and 

 perhaps magnetite (?) are abundant with the zircon and by their 

 alteration furnish the brownish or reddish-brown stain which often 

 gives these colors the surrounding grains. Calcite is also present 

 here, and is apt to be closely associated with the clusters of zircon, 

 frequently embedding them. Closely associated with the calcite and 

 the stained areas, sometimes quite abundantly, are several other prod- 

 ucts evidently secondary. One resembles chlorite. Another com- 

 pact yellowish material has not been identified. The zones in the 

 zircon crystals, particularly the outer zone, are often filled almost to 

 opacity by a fine light brown to red, dusty product. In spots the 

 smaller zircons are also more or less filled with it. What this product 

 is has not been determined. 



The feldspar of the coarser-grained portion is the same microcline- 

 albite-microperthite as that in the granite. Its color is usually a pale 

 greenish-white, although it is sometimes reddish from the alteration of 

 small plates of ilmenite or hematite which occur along the cleavage 

 planes. The crystals are rudely rectangular in outline but always 

 with xenomorphic outlines towards the other minerals. In size they 

 vary greatly, ranging from grains 3 or 4 mm. on a side to ones 1.5 by 

 2 cm., rarely larger. The average probably lies about midway between 

 these figures. As in the granite, the albite strongly predominates 

 about the outside of the grains. Smaller, relatively long and narrow 

 shreds of albite lie in or along the margins and to some extent within 

 the body of the crystals. The usual included microlites of aegirite 

 and riebeckite as well as the minute black particles and cavities are 

 present. A little kaolinization has taken place in portions of the 

 ])egmatite. 



Aegirite and riebeckite are both abundant. Taking the zone as a 

 whole the former is the most plentiful. The riebeckite forms elongate 

 crystals ranging in size fi"om small grains up to large and very con- 

 spicuous crystals, 1 to 2 cm. in diameter and 5 to even 15 cm. in 

 length. The larger crystals are more abundant towards the center 

 and may extend out into the quartz center. Although indented by 

 the feldspar and often including grains of it, the riebeckite, especially 

 in the larger crystals, shows a tendency to develop a crystal cross- 



