II. Ox THE Geology of the New Haven Region, with special 



REFERENCE TO THE OrIGIN OF SOME OF ITS TOPOGRAPHICAL FEA- 

 TURES. By James D. Dana. 



with a map. 



1. The 'New Haven reg;on. 

 Either side of New Haven bay, — an indentation of the coast about 

 four miles in depth, — there is a north-and-south range of hills, the 

 trap and sandstone ridges of East Haven and North Haven on the east, 

 and the eastern portion of the Woodbridge plateau on the west ; and 

 these make the eastern and western boundaries of the New Haven 

 region. Their height, which is greatest to the north, probably nowhere 

 exceeds 600 feet. The width of the region varies from about four 

 miles on the south to seven on the north, and the whole length from 

 the Sound to Mt. Carmel — its true northern topographical limit — is 

 twelve miles. The northern half of the resfion is divided lonsfitudi- 

 nally by two lines of ridges : (1) the long West Rock trap ridge near 

 the western side, four hundred feet and upward in height ; and (2), 

 nearly midway in the area east of West Rock, the short isolated East 

 Rock (E) range of trap and sandstone, and the continuation of this range 

 northward to Mt. Carmel in the low Quinnipiac sandstone ridge which 

 divides the waters of Mill River and the Quinnipiac. The New 

 Haven region hence consists in its northei'n half of three subordinate 

 north-and-south regions; (1) a narrow valley west of West Rock, 

 drained by West River; (2) a broad central plain (the Hamden plain), 

 continuous with the New Haven plain, rising into hills to the north- 

 ward, and drained along the east side by Mill river ; and (3) a wide 

 eastern portion occupied by the river-course and the extensive meadow 

 lands of the Quinnipiac, in other words, the wide valley of the Quin- 

 nipiac. South of East Rock, the central New Haven plain blends with 

 that of the Quinnipiac. The West Rock ridge to the north throws 

 off a branch on the east which curves around to Mt. Carmel and forms 

 the northern boundary of the central of the three subordinate regions. 

 This central region* is partly subdivided across, on a line, nearly, with 

 West and East Rocks, by two short trap ridges ; Pine Rock, (P) a third 

 of a mile from West Rock, and Mill Rock, (M) which adjoins EastRock ; 

 the width of the interval between the two is nearly a mile. Mill 

 River passes through a deep cut in the Mill Rock ridge, at the vil- 

 lage of Whitneyville. A clear idea of the topography of the reoion 



