F. Ward— Lighthouse Granite near Neiv Haven, Conn. 141 



The joint interval varies from an inch or so to several feet. 

 In some instances the joint faces are well slicken sided. Near 

 the fault contact the joints are so numerous and the interval 

 so small that they form an intricately interlaced mass of 

 fractures whose directions it is » FlG 3 



difficult or impossible to deter- , . _^ 



mine. In some places, espe- ^ >-^_ -*- "** ~"~ \ 



ciallv near Lighthouse Point, ^ ^ ^"- — -^^ ^^ 



the joints are curved; some- ^ ^, — ^^^_-^ "^^ 



times these are scattered among ^ ^_ ^ - — - **~ "*^\ 



the regular ones and at other ^" # ^^ - — ■ ^ *^"\ 



times they are in parallel series 



as in figure 3. The arc of the curve is usually small, a foot 

 or so across, but may in a few cases be several yards in extent. 



The character of the joints varies from place to place. A 

 good instance of this is in the vicinity of Lighthouse Point ; 

 the creek (Morris Creek) that separates this point from Morgan 

 Point is a dividing line, — on the west side, Lighthouse portion, 

 the joints are numerous, the interval small, and curved joints 

 are on the whole common ; in many places the rock looks 

 almost shattered ; on the east side the joints are less numerous, 

 the interval is large, curved joints are rare, and the rock as a 

 whole much more massive. 



Faults. — The most distinct fault (or series of faults) is the 

 one separating the granite from the Triassic. The fact that 

 all members of the eastward-dipping Triassic, anterior, main 

 and posterior with the intervening sandstones and shales, in 

 turn abruptly meet the granite is convincing proof of a fault. 

 Additional evidence of movement is furnished by the great 

 abundance of joints near the contact, numerous slickensides, 

 the brecciated character of the contact granite as seen in thin 

 section under the microscope. The displacement has been at 

 least several thousand feet. 



"Within the granite formation itself there is little evidence 

 of much faulting. The massive nature of the granite hides 

 any possible movement. An occasional pegmatite dike shows 

 a throw of a few inches or perhaps a foot or so. Abundant 

 joints and slickensides in certain places prove movement but 

 give no measure of the displacement. Such distinct drainage 

 lines as Stony River, Morris Creek, etc., suggest faulting but 

 do not prove it. Undoubtedly there are many faults as yet 

 unobserved : they can only be proven by the minute scrutiny 

 of the jointing, slickensiding, gneiss planes and drainage. As 

 yet sufficient data have not been accumulated to make definite 

 statements. 



Contact with the Branford Granite. — The Lighthouse granite 

 merges gradually into the Branford granite. There is no dis- 



