522 DAVIS AND GRISWOLD — BOUNDARY OF CONNECTICUT TRIASSIC. 



of these have movements of considerable measure. In spite of this in- 

 visibihty, we confidently believe in the existence of the marginal faults. 

 They need not be more doubted than many others elsewhere whose 

 existence is satisfactorily established on indirect evidence. 



Discontinuity of Triassic Strata.^Alth.ou.gh the faults themselves are 

 nowhere seen, good evidence of their occurrence is not wanting. On 

 approaching the eastern boundary of the formation, south of the Glaston- 

 bury corner, it is found that the Triassic strata are abruptly terminated 

 against the crystalline terrane. This is best seen along the first fault- 

 line, especially in its southern part, where it turns to a somewhat oblique 

 course. Here various recognizable strata of the series, either aqueous or 

 igneous, may be easily followed along their strike by repeated outcrops 

 or by the continuity of essential topographic features, tested by occasional 

 outcrops, and in many successive instances the border of the formation 

 runs at a strong angle with the strike of its members. It is easily con- 

 ceivable that such a relation might follow from the erosion of a series of 

 strata unconformably overlapping an inclined foundation; but this possi- 

 bility is excluded here by reason of the directness of the border line, in 

 spite of repeated changes in the strike and dip of the bordering strata. 

 It is most impressive to follow the sweeping curves of Pond and Totoket 

 ridges,* formed by the main trap sheet, whose great extension is so well 

 proved, and perceive its obedient termination as it approaches the border 

 line. Its strength does not weaken; it is still a heavy flow of lava, as 

 strong a ridge-maker near the border as away from it ; it shows no signs 

 of thinning, as if toward its original margin ; it abruptly stops. This is 

 but a repetition of the lesson of the Meriden district, where the ridges 

 formed on this heavy lava flow so submissively disappear on approach- 

 ing the invisible, but dominating fault-lines. 



As with the ridges of the main trap sheet, so with the minor ridges of 

 the posterior trap sheet and the valleys of the anterior, posterior and 

 upper shales, sandstones and conglomerates. On the ground, where the 

 successive localities are far separated and out of sight from one another, 

 these facts are slowly perceived, but when presented on a map it is very 

 manifest that the curved belts formed by the successive members of the 

 formation, so systematic within the Triassic area, are all cut ofl" at the 

 border as if by some gigantic shearing tool. 



It is not only that the edge lines of the several members of the Trias 

 are cut ofl" at the border, but the dip lines must by inference be cut ofl" 

 underground. If we pass southeastward through the middle of either 

 the Pond Rock or the Totoket crescent, we discover a strongly marked 

 monoclinal structure, with dips averaging twelve or fifteen degrees, pass- 

 ing upward from the lower sandstones and conglomerates, through the 



*The curved southern members of the main trap sheet, figure 1. 



