230 Longivell — Structure of the Triassic 



with relative downward displacement on the west and 

 with no appreciable lateral movement. 



Evidence relating to the second question is very meager. 

 There are some facts to indicate that the great boundary 

 fault on the east side of the Triassic area dips westward, 

 at least in part of its course, and some geologists have 

 assumed that the other faults are generally of the normal 

 type. A study of the diagrammatic cross-sections in the 

 literature, however, reveals striking differences of con- 

 ception. The vertical fault-traces in some diagrams evi- 

 dently represent efforts to appear noncommittal as to the 

 actual attitude ; but a fault which is now vertical may 

 well have had an original eastward inclination, if we 

 conceive that the blocks suffered some rotation during 

 the tilting of the entire Triassic area. In Barren's 

 sections 5 most of the faults are shown as reverse, with 

 a steep inclination of the planes to the east. Evidently 

 this conception is permitted by the surface evidence, 

 which merely indicates that in most cases there has been 

 relative downthrow on the west. Barrell sought an 

 explanation of the general eastward dip of the Connec- 

 ticut Triassic in a geanticlinal uplift along the old Taconic 

 axis, and conceived that during the uplift subcrustal flow 

 from the limb toward the crest might produce shear in 

 the overlying crust, breaking the sediments by steep 

 reverse faults. As the movement continued the blocks 

 would be rotated, and thus some of the faults may have 

 been turned to a nearly vertical position. 6 



There is little probability that this question will be 

 settled by direct observation. It is possible, however, 

 that an accumulation of indirect evidence may lead to 

 general acceptance of one view or the other. Groups of 

 minor faults which appear to be of the "sympathetic" 

 type should give valuable testimony, for they should in 

 general imitate the inclination as well as other character- 

 istics of the major fractures. It is readily seen that the 

 attitude of the small faults at the Saltonstall tunnel favors 

 the view of normal faulting for the Saltonstall basin. 

 The average inclination determined for these planes (67°) 



5 Barrell, J.: Central Connecticut in the Geologic Past, Conn. Geol. and 

 Nat. Hist. Survey, Bull. 23, 1915. 



6 Personal communication. These ideas are also outlined in a manuscript 

 left unfinished "by Professor Barrell. 



