FORMATION OF THE TRIASSIC BASIN. 377 



I have been greatly interested in the hypothesis which lias been 

 advanced and expounded with so much acuteness l)y Prof. W. M. Davis ^ 

 in explanation of the monoclinal faulting, and applied so full}- to tlie south- 

 ward extension of this area across Connecticut, and I have permitted myself 

 to be guided by it as far as possible. This has been, however, rather per- 

 missive than compulsory in this region, for, as just seen, the easterly dips are 

 only slightly in the ascendency. All the strongest dips are to the south, as 

 in the Holyoke range, in Gill and northern Montague, or northwest in 

 central Montague. In several cases submerged peaks and bosses of crys- 

 talline rocks have thi-own off" the sandstones in various directions and have 

 plainly acted rather as resistant masses against which the sandstones have 

 been crowded iiregularly than as masses whose own deep-seated compres- 

 sion has produced a monoclinal faulting in which the sandstones have pas- 

 sively shared. Thus at the mouth of Millers River the rocks have been 

 crushed and faulted against a great mass of most rigid quartzite, and dip 

 strongly west, and a little farther west change suddenly to high south dips, 

 and to the west of Montague village the great mass of uncovered gneissoid 

 conglomerate throws off" the sandstones to the northeast. It would thus 

 seem that in all its northern portion the vallev is too narrow and tortuous 

 and its bottom too irregular and too much broken through by later intrusive 

 plugs of trap to allow of the regular development of this structure. The 

 southern, broader portion of the valley in Massachusetts is too much covered 

 to exhibit fully the system of the faults. 



At the north end of the basin the boundary extending southwestward 

 from the Connecticut is plainly a boundary of erosion, and the conglomer- 

 ates extended formerly nnich farther than at present. Indeed, it leaves the 

 impression that the basin was a strait, extending northward into another sea. 



An inspection of the map will show that the whole width of the Trias 

 across the north of Grill is of conglomerate, equally divided between the 

 arkose on the west and the slate-conglomerate on the east. The lioundary 

 is a narrow, transitional band, rather than a line, but is very distinct. From 

 Bernardston across to the boundary the rock is pure granitic debris; near 

 this line slate pebbles begin to appear, rounded and far-traveled, and soon 

 the finer material comes to be also wholly of comminuted slate and 



'Am. .lonr. Sei., -Sd series. Vol. XXIV, p. 347; Vol. XXXII, p. 342. Bull. Mus. Comp. Zool. 

 Harvard Coll., geol. series, Vol. II, p. 99. 



