MUSEUM OF COMPARATIVE ZOOLOGY. 133 
have been derived from the upper surface of the surrounding trap, or 
from another trap mass above. 
We therefore conclude, in reviewing the examination of the breccias, 
that sand and sandstone grains and a moderate share of rounded grains 
of close-textured normally eroded trap were all filtered together down 
the fissures that traversed the sandstones and trap sheets, and that on 
reaching the points exposed in the quarry they found a confused mass 
of large and small angular fragments of trap, broken from the walls at 
the time the fissures were made, the whole forming a highly character- 
istic breccia. Such breccias are not uncommon in the valley, as at 
Branford, locality 21 (Fig. 17), where they are associated with the great 
fracture by which the formation is bounded on the east; and in the 
Tariffville Railroad cut, locality 13, of minor importance. Percival knew 
a few of them, and called them “clay dikes.” While our conclusion may 
therefore be considered well supported, it must be remembered that 
the breccias do not afford any evidence as to the intrusive or extrusive 
origin of the trap sheets, and are therefore to be regarded as of secondary 
importance in this essay, however valuable they may be structurally. 
Tarifville. Locality 13.—One fourth of a mile east of Tariffville 
station on the Connecticut Western Railroad (Fig. 8), a cut exposes a 
valuable section of the anterior ridge.? The greater part of the cut is 
in massive trap; a narrow band of breccia occurs near its middle. At 
the eastern end of the cut, the upper portion of the sheet shows a thin 
bed of tufaceous material, which locally passes into a bed of trappy 
sandstone along the strike ; and above this there is a second sheet of 
compact trap of moderate thickness, with its upper surface lost in drift. 
’ The two sheets together constitute the anterior ridge at this place. 
There appears to be little if any lithological distinction between them ; 
they are both glassy varieties of augite-porphyrite. The upper surface 
of the lower trap, although generally amygdaloidal, is not so much so as 
is usually the case. Immediately beneath the sandstone layer, the 
amygdaloidal cavities have an aberrant character, being several inches 
in length and generally about one fourth of an in inch in diameter, with 
their longer dimension normal to the surface of the sheet. Amygdules 
in such cavities have been described from one of the extrusive copper- 
1 The relation of these breccias to the faults of the region is more fully dis- 
cussed in a previous Bulletin of this volume, No. 4, p. 77. 
2 See an account of this locality by W. North Rice, in the Amer. Journ. Science, 
XXXIL., 1886, pp. 480-433, where it was first brought to public notice. 
