474 GEOLOGY OF OLD HAMPSHIRE COUiSTTY, MASS. 



From the bend in the brook the npper, highly scoriaceous surface of 

 the trap can be followed north, along east of the fault line and behind the 

 house standing north of the brook. The trap is very deeply rotted. It is 

 a fine example, rare in this region, of a protected pre-Glacial surface. It 

 falls apart now into a mass of spheroidal bodies made up of many very 

 thin concentric layers, a result of rapid cooling. It is the same surface 

 wliich just adjacent is loaded with shale. 



( )n the other hand, going south up the brook from its bend, one finds 

 it running on the trap near its base imtil one comes to its farthest outcrop 

 near the Electric Road. Here the trap rests on the sandstone irregularly, 

 partly upon its basset edges on the west side of the outcrop and partly 

 mantling over to rest on the surface of the upper stratum toward the east. 

 The fault must pass just to the west of this contact. 



THE BLENDING OF THE TUFF WITH THE SURFACE OF THE POSTERIOR BED. 



Beneath the northeastern pavilion in Forest Park (fig. 2.5, p. 4G6, near 

 the east end) the surface of the posterior bed is full of angular fragments of 

 a fine-grained trap, partly compact and partly porous, which are plainly 

 foreign inclusions. They are, however, sometimes fused into continuity 

 with the inclosing trap, as if they had fallen into the molten lava and 

 had been themselves partly remelted. The inclosing trap has a mottled, 

 red-brown, weathered surface, and is covered by small pimph^ knobs, 

 which cause the mottled appearance, and it is so coarse-grained that the 

 white feldspars can be easily seen. It is thus quite unlike the inclosed trap. 

 The old surface of the trap sheet is filled in this way for a distance of 150 

 yards west, to the top of Little Mountain, and 600 yards north. This is 

 quite the same thing as the mingling of mud with the surface of the same 

 sheet just south, at Delaney's quarry, as described on page 470, and indi- 

 cates that the ejected fragments fell upon the surface of the flowing lava 

 here as the mud spread over it farther south. 



A TUFFACEOUS SANDSTONE CONTAINING WHITE TRAP. 



Tliis curious rock appears just above the posterior bed on the north 

 bank of Roaring Brook, a few rods east of the Northampton- Holyoke road 

 and near the line between these towns. It is a sandstone containing many 

 small, angular pieces of a white rock which effervesce freely and seem to 

 be calcite. They prove to be a scoriaceous lava, now filled with secondary 



