THE NEWER CORES AND SMALL DIKES. 495 



posed of the same type of trap and contains as inclusions portions of coarsely 

 amygdaloidal trap, derived doubtless from the posterior trap sheet, or the 

 tuff, through which it has been intruded. 



THE SMITHS FERRY CORE. 



Directly opposite the Smiths Ferry station and at the edge of the low 

 teiTace sands just south of the extensive dog kennels the tuff is interrupted 

 by an area of trap, about 6 rods on a side, which seems to be intruded 

 through the tuff, since it has angular masses of the tuff 6 inches across 

 included in its mass. It does not rise above the level of the tuff, as is usual 

 with the more compact plug trap, and I at first considered it a portion of 

 the surface of the posterior sheet exposed where the tuflP had been worn 

 through, but the inclusions of trap are foreign to the posterior sheet and the 

 erosion of the old lake shore-line may have lowered the plug at this point. 

 (See, however, page 474.) 



CORE AT THE ELECTRIC RAILROAD CROSSING OF ROARING BROOK. 



Where the Holyoke Electric Railroad track leaves the main road to 

 go to Forest Park it crosses Roaring Brook. Just south of this crossing is 

 a sui-face of trap, exposed by the excavations for the road, which is weath- 

 ered and breaks up into spheres at the surface and rests on the sandstone 

 in the brook just below. This is the south exposure of the posterior trap 

 sheet. Just across the brook the railroad cutting exposes a splintery trap of 

 fine grain and perfect freshness, which seems to be the southernmost of the 

 small plugs accompanying the posterior sheet. 



8TJM3IART OF HISTORY OF THE CONNECTICUT RIVER SANDSTONE. 



The mountain-making forces which folded up the Appalachian chains 

 acted against the mass of the Archean rocks in the Adirondacks, as seen 

 by the great curve which these chains make as they run southward beyond 

 its influence. The outlines of the Connecticut Basin were laid in pre- 

 Devonian time, since the Bernardston Devonian is bordered by shore con- 

 glomerates which coincide with the borders of the basin and the later limits 

 of the Trias. The sinking of the great block south of the Connecticut 

 shore-line, which broke this curve of the Appalachian chains, prepared the 

 way, perhaps, for the second admission of the waters into this narrow 

 channel, which in shape and position resembled the Bay of Fundy. 



