204 On the Trap Tuff of the Connecticut Valley. 



structure 



to convert them into a scoriaceous mass ; or if the organic mat- 



space 



as 



by the gas resulting from the decomposition of the organic com- 

 pounds. 



anic 



rock, and thus might volcanic matter be made to take a stratified 

 structure ; but when quiet was again restored on the ocean's bed, 

 new deposits of sandstone and shale would take place. After all 

 this, the principal eruption of trappean matter might take place 

 along nearly the same line, and the principal ridges of unstrat- 

 ified trap be protruded, and the sandstone and bedded trap, at least 

 in the vicinity, be tilted up. 



Now in respect to the sandstone and tufaceous rock of the val- 

 ley of the Connecticut, we have the most decided evidence that 



been 



amorphous nages 01 

 I have stated that 



the general dip of the sandstone in the valley is 15° or 20° easterly, 

 both below and above (or west and east of) the trap ridges ; and the 

 fact that it is nearly the same below as above, shows conclusively 

 that this general dip was not produced by the protrusion of the 

 greenstone : for how could that elevate strata lying beneath it ? It 

 must, therefore, have been originally deposited with its present dip, 

 or elevated by some other agency than the trap. But on the upper 



exam 



strata have been elevated very much more than the general dip; 

 which greater slope, however, dies away as we recede from the 

 trap. Take for an example, the section given on fig. 2 ; which 

 crosses Mount Holyoke near its east end from Amherst south- 

 easterly into Belchertown. Beneath the trap the dip is as usual; 

 but on passing over the ridge, we find the strata dipping prettV 



, _ & „„._--W 



turned aside 45° from the usual course. The deposit of trap 

 tufa, which is crossed by the section, shares in the increased dip- 

 Now it is not possible that sandstone, most of it rather coarse, 

 should have been deposited on a slope of 50°. It must have been 

 tilted up after its deposition, and consequently after the deposi- 

 tion of the tufaceous rock. At the other beds of this rock, the 

 dip is not much greater on the upper than on the lower side ot 

 the principal trap range. But along the south side of Holy<^ e 

 generally, the dip is southeasterly, although not usually more 

 than 20° ; and I see not how this can be explained except by im- 

 puting it to the protrusion of the trap range in a direction a 

 right angles to the usual strike of the strata of sandstone. 

 Near the northern extremity of the sandstone formation in 



this 



another exam 



and 



