524 DAVIS AND GRISWOLD — BOUNDARY OF CONNECTICUT TRIASSIC. 



It is to the weakness thus engendered that we attribute the disappearance 

 of the anterior trap ridge in the southern part of this crescent. The 

 southern end of the posterior trap ridge is much obscured by heavy 

 drift, and nothing can be said of it ; but near the middle of the Pond 

 Rock crescent, along the Triassic border in the village of Branford, there 

 is a second posterior ridge, and this has already been interpreted in ear- 

 lier papers as a reappearance of the same trap sheet that forms the first 

 posterior ridge. A close examination of the ground does not, however, 

 confirm the relatively symmetric reversal of dip indicated in earlier 

 figures, and hence it is concluded that this second ridge is formed of 

 large fragments or blocks of the posterior trap sheet that were caught in 

 the fault. The varying attitude of the trap sheet, as inferred from the 

 position of its dense under surface and its vesicular upper surface, as 

 well as the plentiful breccia of angular trap fragments with sandstone 

 matrix, give support to this conclusion. Outcrops in this neighborhood 

 are, however, very few. Further north, near Middletown, there is much 

 irregularity of dip and strike in the sandstones near the margin, such as 

 never occurs within the area of the formation except in the neighborhood 

 of fault-lines. North of Glastonbury the Inarginal outcrops of Triassic 

 strata are so rare that no sound conclusion can be based on them alone. 

 Alteration of Crystallines along the Border. — The old crystalline rocks 

 present characteristics along the meridional part of the Triassic margin 

 which are not common to these rocks elsewhere. The fact that the gen- 

 eral strike of the old gneisses and schists is about northeast and south- 

 west, thus giving a considerable angle of intersection with the meridional 

 fault-lines, makes it possible to associate changes in the characters of 

 rocks along their strike-lines with the explanation of the border line 

 itself. The greater development of chlorite along the border line is a 

 marked feature throughout. Microscopic examination shows that the 

 crystals of different minerals are commonly broken. In many places 

 the simple gneissic or schistose structure has been lost, and the rock 

 appears twisted and broken. The rock thus affected may still remain 

 in this crushed condition, presenting a loose fault breccia, as at the 

 quarry for road-metal at South Glastonbury ; or it may be re-cemented 

 into an exceedingly tough rock by quartz or chlorite, or sometimes by 

 barite. The rock thus formed seems to be much more enduring than 

 many of the unmodified members of the old crystallines, yet special 

 search among the Triassic conglomerates has failed to reveal its presence ; 

 hence it is thought to be of later origin than the conglomerates. The 

 alteration of the crystallines has been made out clearly only along the 

 meridional portions of the Triassic border. It is less distinct along the 

 oblique portions. This, however, might be expected, even if faults occur 

 there, for the reason that movement near the plane of foliation would 



