MUSEUM OF COMrARATIVE 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 ai-e 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. 



Tariffville. Locality 13. — One fourth of a mile east of Tariffville 

 station on the Connecticut W^estern 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. 



"^ See an account of tliis locality by W. North Rice, in the Amer. Journ. Science, 

 XXXII., 1886, pp. 430-433, where it was first brought to public notice. 



