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



tinct line of contact, there are all transitions from the one kind 

 into the other : there are no stringers or dikes of one kind 

 leading into the other ; there are no inclusions of one in the 

 other.. These facts, taken into consideration with the fact that 

 both granites are very much alike mineralogically, chemically, 

 etc., show that the two are synchronous in origin, — they are 

 both phases of the same original magma. 



Age and General Relations. 



It is impossible to determine definitely the age of this rock. 

 The only formation in the region w T ith a known age is the 

 Triassic, and the arkose there is distinctly derived from this 

 and related granite areas ; hence the granite is older than the 

 Triassic. It is known to be an integral part of the Lighthouse- 

 Branford-Stony Creek intrusion, which is in turn one of the 

 many New England granitic masses. Kemp says* the Con- 

 necticut and Rhode Island granites are Post-Cambrian and Pre- 

 Triassic. Dale statesf that the Maine granites are Late Silu- 

 rian or Devonian in age. 



Nothing more definite can be said until the age relations of 

 other Connecticut formations are better known. 



*Bull. Geol. Soc. Amer., x, 372, 1899. 

 fU. S. G. S. Bull. No. 313, p. 11. 



