470 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



Along the eastern margin of this basin the outcrop) of the trap sheet 

 is plainly visible, covered by tuff and marked at its base by a prominent 

 talus. As it is followed south its boundary makes a great loop to the east, 

 where the ridge is cut through by a brook, but rises again in a higher bluff 

 south of the brook, now marked by a high trestlework lookout-tower. The 

 contact on the sandstone below is everywhere normal — the compact trap 

 rests on unbaked sandstone — until the boundary swings around the south 

 end of this prominent hill to a point w^hich rises sharply in a bluff 30 rods 

 north of where Roaring Brook crosses the road. This is the brook that 

 comes up from the south and bends sharply to enter the Connecticut 

 southeast of Mount Tom. Delaney's quarry, described below, is situated 

 just south of its mouth, between the road and the railroad. 





Fig. 26. — Section of Delaney's quarry, in Northampton, near the nortli line of Holyoke, on the Connecticut River Railroad. 



The base of the trap sheet in this bluff is scoriaceous and filled with 

 sheets and filaments of limestone and shale exactly like the surface of the 

 trap a few rods south at the quarry mentioned above, so that I am compelled 

 to assume that a portion of the surface has here been under-rolled to make 

 the base 



The conditions here are so peculiar that they require detailed discus- 

 sion, which may best begin with a detailed description of the quarry east 

 of the fault, returning then north to the south bluff section, which can be 

 best explained by a comparison with the conditions at the ([uarry. 



delaney's quarry, near the north line of holyoke. 



This is a good example of a deeply submerged lava surface onto which 

 much mud was washed while it was still plastic (see fig. 26). Many masses 

 of the mud, varying from thin filaments a few inches long and a small 



