F. Ward — Lighthouse Granite near New Raven, Conn. 135 



and from a fraction of an inch to six or eight inches in width. 

 They may cut the rock in any direction, but in a few cases are 

 found to have a trend parallel to the joints of the locality. 

 At several points these veins are large, that is are measured 

 by yards rather than by feet or inches. 



Inclusions. — In places and spots throughout this granite 

 occurs a material which is different from the normal granite 

 or pegmatite. It is a well-banded gneiss and may best be 

 described as a biotite-gneiss injected with granitic magma. 

 The injection varies from thin lines of pinkish granite material 

 to broad (half-inch) layers of distinct granite. The granitic 

 magma has entered the gneiss along its natural structure planes 

 for the most part, accentuating the original gneissic structure, 

 but sometimes has cut across the whole in any direction. The 

 development of large orthoclase crystals has bent the planes of 

 the gneiss out of alignment ; these large feldspars give the 

 rock in some places a porphyritic appearance Most of the 

 specimens are over fifty per cent granitic magma, but, on the 

 other hand, some of them are apparently not injected at all. 

 In shape they may be slab-like, or they may occur in small 

 pieces or large blocks. They vary in size from a few inches 

 to several yards in diameter. Their outlines, while distinct, 

 are not sharp. 



This gneiss is an older rock as is shown by the fact that it 

 occurs as irregular masses or blocks included in the normal 

 granite, and also by the fact that in places the injections of 

 magma can be followed back into the enclosing granite. 

 It is believed that these included masses are modified frag- 

 ments of the country rock into which the granite mass as a 

 whole was intruded ; they resemble very closely the Middle- 

 town gneiss, which occurs in place several miles to the 

 northeast. 



The inclusions occur very sparingly in- the western half of 

 the Lighthouse granite and are not abundant, on the whole, 

 even in the eastern part. They are seen well at Mansfield's 

 Grove, also at a point upwards of a half mile north of the 

 Grove along the road. 



Contact Phase — There are a few places at or near the con- 

 tact with the Triassic where the rock has an appearance dif- 

 ferent from that already described. In the first case the rock 

 is denser and has a greenish material (chloritic) scattered 

 through it in streaks and smears or occurring in thin dike-like 

 planes following the joint directions. Secondly, the rock may 

 be quite broken in appearance, due to the presence of many 

 sets of intersecting joints, and may approach the character 

 of a true breccia. Or lastly the rock may be whitened or 

 bleached — the result of greater alteration along a fractured 

 zone. 



