Massachusetts, (Jomn-eth-ut i< ml X> tc Jersey. 347 



within the mass or at its base ; they exert a small metamorphic 

 effect on the underh iug siratum, and none at all on the over- 

 lying bed which was deposited conformably upon them. They 

 are sometimes accompanied by a tufaceous deposit, presumably 

 of ashes thrown into the Triassic estuaries; and the overlying 



overflows aie the Tun r's h s-De, field Range, as lately 

 shown by Emerson : Mts. Holyoke and Tom, first proved by 

 Hitchcock, and their extension' southward into Connecticut to 

 the Hanging Hills at Meriden ; Lamentation Mountain and 

 some others to the south of it, with their subordinate lateral 

 ranges nearly to Long Island Sound; and First and Second 

 Newark Mountains in New Jersey. The evidence is not 

 equally complete for all of these. 



The general history of these Triassic deposits seems to be as 

 follows : Their strata were laid down about horizontally ; 

 Rogers' suggestion that their pivs. nt dip comes from an ong- 

 ]I1 al oblique deposition cannot be adopted. During their accu- 

 mulation, heavy sheets of trap overflowed their surface, and 

 sometimes rose above the Triassic waters, so that fragments of 

 trap were mixed with the next formed' beds. The common 

 occurrence ol' foot-prints in the strata not far above the trap 

 is, as was shown Hitchco.-k, a similar confirmation of this 

 Point. These eruptions did not occur simply because the 

 region was disturbed, for many regions of much greater dis- 

 turbance show no igneous rocks ; but very probably because 

 i-bance was a downfolding and not a general upfolding 

 ; '- s in most mountain ranges. The deposition ol' more strata 

 and the overflow of more trap ceased when ih< dowufohtmg, 

 that had begun and deepened the Triassic troughs, changed 

 (for some unknown reason) to disturbance with uplifting. 



The general monoclinical structure of the several Triassic 

 belts is not considered the result of original oblique deposition 

 as proposed by Rogers ; or of bi og as sug- 



gested by Kerr and Russell; or of a simple monoelinal tilting 

 I by Hitchcock and LeGVmte: but is regarded rather 

 as the effect of lateral compression, producing a peculiar dis- 

 tortion. The style of the distortion is best recognized by 

 Cleans of the overflow trap ridges, which are generally con- 

 tinuous for several or many miles : for these, when once proved 

 verflows, are established as well marked horizons in the 



T: 



<e can thus be obtained to show that the strata as a whole 

 ■e both folded and faulted. The folds take the form of shal- 

 >w oval dishes or boats, of erentle curvature, canted over a 

 ttle and faulted on the side of tin 1 j. • i-ral monoelinal dip ; 

 ud the outcropping c<l-'s of the hard trap sheets then neces- 



