528 DAVIS AND GEISWOLD BOUNDARY OF CONNECTICUT TRIASSIC. 



better shown in the crystalHnes than in the Trias, for although the in- 

 ternal fault with which number 4 is supposed to be continuous has a 

 throw of about 1,000 feet and is a branch of the great Lamentation fault, 

 yet where last identified in the Trias it is a dozen miles from the corner 

 at Vernon. The span of fifteen miles from one point of evidence to an- 

 other may test one's credulity severely, but if the line be thus drawn it 

 is found to coincide in direction with the established parts, which have 

 a total length in crystallines and Trias of about 35 miles ; furthermore, 

 its nearly parallel relation to number 2 is maintained. The two lines 

 diverge very little as they continue northeast. As in the case of num- 

 ber 2, an explanation of the measurement of the two fault systems will 

 strengthen belief in the inference of their occurrence. 



Another explanation of the Contact Line considered. — It might be argued 

 that the marginal line in question is one of continuous fault of irregular 

 trend instead of a combination of five faults, as urged in the preceding 

 section. Let us consider the difficulties of this idea. First, the irregular 

 shape of the line, with its four angles at South Glastonbury, Highland 

 Park, Vernon and Rockville, is in opposition to the generally straight 

 trend of faults within the Trias. It is true that the southern part of 

 number 1 is somewhat irregular, but there are no such sharp changes 

 as at the corners noted above. Second, why should two of these abrupt 

 changes in direction happen to come just where Triassic faults reach the 

 margin ? Mere coincidence would be extraordinary. Third, if so great 

 a fault as number 1 passed along parts 2 and 4, even though coinciding 

 in strike with the strike of the crystalline rocks, field observations should 

 have given unquestionable evidence of movement or metamorphism. 

 Fourth, it seems possible to distinguish a relation between the values of 

 1, 3. and 5 by the amount of crushing and metamorphism that has taken 

 place. Thus 3 and 5 are noticeably lines of lesser disturbance than 1, 

 and 5 would seem to be somewhat greater than 3. 



Measurement of the Faults. — With the above difficulties in the way 

 of the one-fault idea, if we can strengthen the combination plan by an 

 hypothesis of effective quantitative working, we may reasonably give it 

 the preference. Fault number 1 we conceive to continue northward from 

 South Glastonbury, South of 'this point the crystallines comprise the 

 surface rocks on the east side of the line, and from these crystallines 

 has been eroded all the Trias that once extended there, and some of 

 the crystalline foundation as well. Why do the crystallines not continue 

 at the surface north of this point? Because an oblique fault, with a 

 downthrow of about 2,000 feet on the northwest side, intersecting here, 

 has brought the Triassic foundation plane below the present Triassic level 

 of erosion. The present Triassic level is about 600 feet below the level of 



