MESOZOIC TJJVIE — -TKIASSIC AND JURASSIC. 807 



finally, at the time of upturning, the trap and sandstone, thus interstratified, were forced 

 up into monoclines, which by denudation became the existing trap ridges. 



According to the views already presented, (1) the trap mass in the trap ridges may be 

 conformable, or not, to the associated sandstone ; and (2) the supply fissure was near the 

 eastern base of the ridges, or not far distant. These conditions are illustrated in Figs. 

 275, 276, on page 302. In the views of W. M. Davis, on the contrary, (1) the trap mass 

 of the ridges is conformable with the sandstone and with its other trap sheets ; and (2) it 

 extends to the east and west of the ridges as a conformable sheet in the sandstone forma- 

 tion, and should be found there by boring if not exposed at surface. 



It is favorable to this hypothesis that the sandstone is admitted to be in monoclines ; 

 that the trap ridges look like monoclines, the trap and sandstone so far as exposed to 

 view being eastward in dip ; that the greater trap belt and the smaller attendant belt on 

 the east and west have the ]Dositions in the external view that correspond to layers in a 

 monocline ; that in some regions the beds of the sandstone formation underneath the 

 columnar trap in the front of trap ridges have a like order of succession. 



But it is unfavorable to it that the hooked or bow-like shapes among the ridges are not 

 such as are characteristic of monocliual regions ; that the varying dip of the sandstone 

 within the bow — it being nearly at right angles to the direction of its sides and ends — 

 is an exceptional feature for monoclines, and an actual feature of those trap ridges which 

 are admitted by all to be eruptive. It is also unfavorable that no outcrops of either of the 

 three conformable sheets of trap have been observed along the eastern margin of the area ; 

 that no sections of the sandstone formation occur anywhere in the part of the area east 

 of the Connecticut River, which exhibit the conformability of the ti'ap sheets with one 

 another or with the sandstone, or that show any trap at all ; that no sections exhibiting 

 conformability have been observed in any of the trap ridges themselves, and none over 

 the part of the Triassic area west of these ridges. Thus positive evidence in favor of the 

 hypothesis fails ; and there is the evidence against it that the Saltonstall region, instead of 

 exemplifying it, as claimed by its author, is a region of eruptions after the upturning 

 of the sandstone, and that the Mount Tom Ridge bears the strongest evidence of a 

 laccolithic origin. 



The existence of buried volcanoes at Mount Carmel (740' high), 9 miles north of New 

 Haven, has been announced. But there is no evidence of the "buried volcanoes" in 

 sight : neither in lava streams, volcanic ashes, nor anything else. The rocks in view are 

 the ordinary compact trap of the trap dikes of the region and the intersected granitic 

 sandstone. 



Origin of the eruptions. — Although the geosynclines or troughs in the 

 earth's supercrust occupied by the deposits were comparatively shallow, 

 none probably exceeding in depth 10,000 feet, the lateral thrust from the 

 opposing directions produced, at intervals, fractures and movements, if not 

 also crushings, at considerable depths for the whole length of the Eastern 

 Continental border, from Nova Scotia to southern North Carolina. For, 

 according to existing theory, the region of fusion was where the earth's 

 interior temperature was so near the fusing point of the rock, that the heat 

 from dynamical sources, added to the statical heat of the region, would produce 

 fusion. The near uniformity in the kind of ejected rock, through all the 

 Triassic areas, has been already mentioned as other evidence that the fissures 

 descended below the supercrust to regions where basic Archaean-like rocks 

 prevail. The ejection of rocks of the basaltic type alone may, however, be a 

 consequence of the temperature not being high enough to melt the less fusible 

 rocks containing oligoclase or ortlioclase. 



