Deer field Trap Sheets are Contemporaneous Flows, 147 



mi 



T, Trap ; Tt, Trap agglomerate 

 with trap cement; Ts, Trap ag- 

 glomerate with sand cement ; S, 

 Sandstone. 



The explanation of this, I believe 1. Trap Section, Greenfield. 



to be, that like an unrolling carpet 



the slaggy surface of the flow was 



underrolled on a submerged or 



muddy bottom and the mud was 



forced up into the fissures by the 



weight of the 200 feet of trap, and 



met in the cracks by the still liquid 



trap from above. 



3. The Holyoke sheet from its 

 east end to the Connecticut River 

 bakes the sandstone on which it 

 rests and has rarely large long steam 

 pores running up from the base six 

 inches or a foot, caused by the moist- 

 ure in the subjacent sandstone, and 

 it is highly vesicular and without 

 any trace of baking at its upper sur- 

 face. 



Between the Connecticut and 

 Westfield rivers (fourteen miles), the base of the sheet is often 

 very vesicular and kneaded full of dove-colored limestone, as if 

 limestone and trap had been plastic at the same time. In 

 thin sections the fine grained limestone can be seen penetrat- 

 ing the steam holes with a distinct flow structure, but the 

 boundaries are sharp between trap and sandstone. The trap 

 is here perhaps 300 feet thick, but has not baked the sub- 

 jacent arkose at all. At one place where the railroad between 

 Westfield and Holyoke cuts the south line of the latter place 

 a broad area of the upper surface of the sheet is filled in the 

 same way with the same limestone to a depth of 8 or 10 feet. 

 This latter rock is not in place in the rocks cut through by the 

 trap, either at the surface or in the many artesian borings I 

 have studied, down to 3500 feet in depth. I explain the above 

 structure also by the underrolling of the surface of the sheet as 

 above. A limited amount of calcareous mud was washed onto 

 the submerged surface of the advancing sheet (which was super- 

 ficially solidified) and blended more or less with this surface 

 which by the continued advance of the mass became in part 

 underrolled, thus protecting the sand below from baking, and 

 bringing the highly vesicular trap loaded with limestone to the 

 base of the bed. 



4. At the Delaney's Quarry by the railroad on the north line 

 of Holyoke the extremely irregular surface of the trap which 

 rises and falls twenty feet in the quarry and is warty and ropy 

 in the extreme, is closely fitted by the dark mud at first depos- 

 ited, and the sandy layers immediately above undulate in and 



