146 B. K. Emerson — Proofs that the Holyoke and 



Art. XIX. — Proofs that the Holyoke and Deerfield Trap 

 Sheets are Contemporaneous Flows and not later intru- 

 sions ; by Ben K. Emerson. 



In the concluding paragraph of his most interesting article 

 on the Trap Rocks about New Haven,* Professor Dana is in- 

 clined to make the results he has reached regarding the traps 

 and sandstones of the New Haven region general for those of 

 the whole Connecticut Yalley. 



He concludes that these traps are subsequent to and intrusive 

 in the sandstones and not " poured out in one, two or more 

 horizontal sheets, separated, and overlaid horizontally by beds 

 of sandstone." The essential point in this contention, if I 

 understand aright, is that the traps associated with the Triassie 

 sandstones are all newer than these sandstones. 



The following is presented as an abstract of the proofs that 

 all the main trap sheets in Massachusetts are contemporaneous 

 flows, and easily distinguished from the smaller intrusive 

 masses. 



1. At the upper surface of the Deerfield bed of trap east of 

 the mouth of Fall River opposite to Turner's Falls, a perfect 

 ropy surface of flow is exposed and the soft red shale folds 

 round the curved surfaces and into the deep grooves in a way 

 only possible by a surface flow. The red sand can be picked 

 out of open steam holes on the surface, as the bed is strongly 

 vesicular at surface. , At the base it is here aphanitic and the 

 sandstone is baked into a black hornstone-like mass. 



2. At the base of the same bed several miles south in 

 the north edge of Greenfield, the cliff has been cleared at 

 the City's Stone Crushing Works and a very remarkable sec- 

 tion is exposed (fig. 1). The dip is east, and in the westward 

 facing cliff the heavy trap bed, 2] rests on soft unbaked 

 sandstone, 3, and is vesicular and coarsely brecciated for about 

 12 to 16 feet. The low r er portion of this agglomerate, Ts, is 

 cemented by a red sand which penetrates the fissures between 

 the breccia blocks for six or eight feet up from the base 

 and is now hardened to red sandstone, which is continuous 

 below with the sandstone on which the trap rests, while an 

 aphanitic non-vesicular trap is continued down between the 

 coarse porous blocks, Tt, from the unbrecciated mass above 

 to fill the fissures down to the point reached by the sand. 



*This Jour., xlii, p. 110. 



