140 F. Ward — Lighthouse Granite near New Haven, Conn. 



would have to form minerals, such as tourmaline, beryl, 

 fluorite, etc. These zones, then, would be temperature and 

 pressure zones and would be more or less horizontal in 

 position. 



Under this theory, then, pegmatites that were an integral 

 part of the rock as a whole and were formed practically 

 synchronously with it, would not be mineralized, while those 

 parts of the pegmatite which forced out or reached up into the 

 very upper portions of the magma or even into the overlying 

 rocks, would be mineralized. If the surrounding country rock 

 were super-heated, those portions of the pegmatite nearest the 

 parent magma would show less mineralization than those 

 portions farther away, etc. 



This theory is only offered as a suggestion. 



The texture of the pegmatite varies from a very, coarse 

 granite to that degree of coarseness where single feldspar 

 crystals are eight inches long (seen well at Mansfield's Grove). 



Quartz Veins. — In the small type of quartz vein the quartz 

 is usually glassy and more or less clear ; in the larger type it is 

 usually whiter and duller ; either kind may be stained brown- 

 ish or reddish by iron oxide. The larger also usually has more 

 or less feldspar present. 



These quartz veins in origin are closely related to pegmatite. 

 It is a well-known fact that quartz veins are the " end prod- 

 ucts, " so to speak, of pegmatite and this region should be 

 no exception. The fact that pegmatites occur whose central 

 portions are pure quartz, and that quartz veins occur with a 

 great deal of feldspar, points to the close relation between the 

 two. 



Steuotuee. 



Gneiss Planes. — These do not always show distinctly and 

 may be so nearly absent as not to show even in a large-sized 

 hand specimen. Their general strike is northeast and south- 

 west, with local exceptions. Their dip is towards the north- 

 west and varies in angle from 0° to 30° ; in the western half 

 of the area they are flatter, averaging 10°, while in the eastern 

 portion they are steeper, averaging 20°. 



Joints. — Joints are very common ; any outcrop will show 

 from one to six or eight sets. There is hardly a direction of 

 the compass that has not a joint direction to match it some- 

 where in the region. But the most common directions (reading 

 only to the nearest 5° angle) are as follows : N. 5° E., _N". 15° E., 

 K 35° E., N. 40° E., 1ST. 60° E., 'N. 85° E., N. 5° W., K 10° W., 

 1ST. 20° W., 1ST. 65° W., K 70° W., 1ST. 85° W. Joints that are 

 practically horizontal are fairly common as well. 



