304 BULLETIN OF THE 



ence is known by the repetition of outcrops that they produce, and this 

 test can hardly be applied as yet in the Triassic belts, for the beds there 

 are, as a rule, too little varied to be recognized at their repeated appear- 

 ances, if such occui'. On the other hand, as may be inferred from the 

 position of the intruded sheets, there is evidence that, however numer- 

 ous the faults may be, they fail to bring up the lowermost strata ; and 

 the great sweep of the trap curves in New Jersey would indicate an ap- 

 proach to the simple monoclinal structure. These considerations would 

 imply a great thickness for the sandstone. (See figs. 6 and 28.) 



The Fourth Theory looks on the general monoclinal dip as the result 

 of tilting with faulting and some slight folding, but is unable to explain 

 the mechanism of the disturbance ; and here with regret I must take 

 my place. Much more observation is necessary before any detailed ex- 

 planation of this peculiar disturbance can be made. It can now be said 

 only that the disturbing force pretty surely was one of the latest mani- 

 festations of the Appalachian mountain-building, which began and had 

 its greatest activity long before ; and that the eruption of the trap had 

 no important share in it. Here, as in so many other cases, the trap is 

 relegated to a passive rule; and as already suggested, its eruption was 

 very probably a direct effect of the force which at one time depressed 

 the Triassic troughs, and later deformed the rocks collected in them. 



It is sometimes objected that it is mechanically impossible to fault a 

 series of horizontal layers into repeated parallel monoclinals. In an- 

 swer to this it should be urged that too little is still known of geological 

 mechanism to make such apparent impossibilities of much importance ; 

 that faulted monoclinals of gentle dip have been found in the Western 

 plateaus (see Button's sections of the High Plateaus of Utah), and oi 

 steeper dip in Tennessee (Safford's Geology of Tennessee) ; and that the 

 Triassic monoclinals show not infrequent irregularity too great to be 

 considered the result of eddies (as Rogers thought), and implying the 

 presence of incipient folds. 



As to the occurrence of faults, some of small throw are seen in Delany's 

 Quarry above Holyoke (B), in the West Springfield railroad cut (C), and 

 on the northern slope of Garret Rock, Paterson (L) ; slickensides are 

 noted about New Haven, in the Jersey City cut, and in Goat Hill by 

 Lambertville. Faults are also shown in the Richmond coal field syn- 

 clinal by W. B. Rogers and Heinrich, and are suspected by Cook in New 

 Jersey (c, 33). Further observation will surely discover others, either 

 directly or by means of repeated outcrops. In this latter way a fault 

 has been determined with a great degree of probability at Beckley, 



