F. Ward — Lighthouse Granite near Nevi Haven, Conn. 131 



Art. XVI. — On the Lighthouse Granite near New Haven, 

 Connecticut ; by Freeman Ward. 



Introductory Note. — The Bran ford granite-gneiss has here- 

 tofore been considered a single unit of like character through- 

 out.* While in a general way this is true, yet, from a closer 

 investigation in both the field and laboratory, it has seemed 

 reasonable to make a separation of the mass into two types — 

 the Bran ford granite and the Lighthouse granite. The differ- 

 ences between them, while not great, are yet thoroughly con- 

 stant. It is proposed in this paper to consider the latter of the 

 two types. 



Location and Topography. 



The formation in question is situated on the coast of Long 

 Island Sound, near New Haven, Conn. Lighthouse Point, on 

 the east side of New Haven Harbor, is its most westerly point. 

 From there it extends east to Branford Harbor (four miles in 

 a straight line). In width (north and south) it varies from a 

 half mile to over a mile and a half. The accompanying map 

 (fig. 1) will show its position and extent. On the north it is 

 bounded by the Triassic formation : the contact line between 

 them starts at the south part of Morris Cove, passes east and a 

 little north to the south end of Beacon Hill ; from there it 

 extends northeast towards a point on the Shore Line division 

 of the New York, New Haven and Hartford railroad, about 

 a half mile west of the Branford station. On the east it meets 

 the Branford granite ; the contact between them passes up 

 through Branford Harbor, keeping about a quarter of a mile 

 west of Branford Point till it reaches just beyond the trolley 

 tracks, then passes northwest to the Triassic. On the south 

 and west the formation passes into the Sound and New Haven 

 Harbor respectively. 



The topography is not striking, that is, there is little relief ; 

 the highest point in the formation has an elevation of only 120 

 feet, and fully one half has an elevation of 20 feet or less 

 above the sea. There are many marshy areas, which are for 

 the greater part flooded by a few inches of water at high tide. 

 The shore line is quite irregular with many small bays, inlets, 

 points, peninsulas and off-shore islands : one large bay opens 

 off of Short Beach. The shore from Lighthouse Point to Mans- 

 field's Grove is made up in a broad way of a series of arcs 

 convex inland. The greater part of the shore has well-exposed 



* W. N. Rice and H. E. Gregory, Manual of the Geology of Connecticut ; 

 Conn. State Geol. Nat. Hist. Surv., Bull. No. 6, 146, 147, 1908. 



