On the Trap Tuff of the Connecticut Valley. 201 



Fig. 2. 



Sand- Trap 

 Sandstone. Trap, stone, tufa. Sandstone. 



Section across Mount Holyoke southeasterly. 



sandstone. I say for the most part; because when the mass 

 is considerably thick, the west or the lower portion of it, is 

 usually distinct greenstone, having no more stratification than 

 trap in any other position. And so in the amygdaloidal and 

 scoriaceous varieties, the stratification is indistinct, and indeed, 

 in proportion as the igneous agency predominated, the rock loses 

 its division into layers, and exhibits it where the aqueous agency 



predominated. 



It ought also to be stated, that the amygdaloidal, scoriaceous, 

 and porphyritic varieties of this rock occur of considerable thick- 



ranges 



extent they are stratified. The brecciated variety is, also, com- 

 mon, capping and underlying the columns, in various parts of 

 the range. I have never, however, found the tufaceous conglom- 

 erates and sandstones as a part of the main range of trap, unless 



We 



[glomerate and 



Topography. 



Nearly all the examples of this rock which I have discovered, 



Holyoke and Tom 



Mounts 



an 



Massachusett 



in Connecticut. Starting at Belchertown, we find the ridge run- 

 ning nearly west for several miles, then turning south to Connecti- 

 cut river, and forming Mount Holyoke. Continuing across the 

 r *er, it rises into the still higher ridge called Mount Tom ; and 

 t} *nce in a lower ridge, into Connecticut. The top of this whole 

 r "*ge is common trap, prismatic, amygdaloidal, and scoriaceous, 

 ^sting upon thick bedded sandstone, which crops out upon its 



eaceous 



Now it is 



*nhin this great curve of the principal trap range, and on its back 

 «fe, that all the deposits of trap tuff, with ^hich lam acquainted, 

 Ooc *. Three of these are shown on the map, Plate I, on the 

 *Mh side of Holyoke, in Granby and South Hadley. I here 

 U a y be others there : but the country being chiefly covered with 

 *«* woods, it is difficult to explore it. On the opposite side of 

 Connecticut river, a still larger deposit occurs in INorthampton, 



Sl co5» 8iri M> Vol. IV, No. It. -Sept., 1847. 26 



