THE TRIASSIC PERIOD. 



23 



is repeated or offset, with or without overlap or gap, according to the relation 

 of the direction of the fault plane to the dip and strike of the rock. 



There is one condition under which an outcrop of the trap may be curved, 

 even when the strata are not deformed. If the surface be in that stage of erosion 

 where the trap constitutes a ridge, the outcrop of the trap will bend in the direc- 

 tion of dip wherever it is crossed by a valley; for here the ridge (outcrop) is 

 lower than elsewhere, and lowering the surface of a dipping stratum always 

 shifts its outcrop in the direction of dip. 



All of the principles here set forth find illustration in the trap outcrops of 

 the Newark series of Connecticut. The faults which are supposed to explain 



Fig. 333. 



Fig. 334. 



Fig. 333. — Illustrates the effect of oblique faulting on outcrops. The more the 

 direction of the fault plane departs from the direction of dip. the greater the over- 

 lap (or if the opposite side had been the downthrow side, the greater the gap). 



Fig. 334. — Diagram illustrating the effect of a gentle syncline, in beds of monoclinal 

 structure, on outcrop, when the surface is plane. 



the relations of the trap outcrops to one another have not all been seen, but the 

 faulting is inferred from the relations of the trap sheets. Each outcrop of 

 trap does not therefore mean a separate flow of lava. Three principal sheets 

 of lava (all extrusive) seem to be represented by the many outcrops. Asso- 

 ciated with these there are minor ridges of intrusive trap. The faulting in the 

 Newark series of Connecticut has perhaps been most carefully worked out in 

 the small isolated area near Pomperaug. Fig. 318 shows the outcrops of one 

 bed of trap, and Fig. 319 that of another. In this small area, containing only 

 about fifteen square miles, the number of faults is said to be more than 250. * 



Hobbs, 21st Ann. Rept. U. S. Geol. Surv., Pt. III. 



