On the Trap Tuff of the Connecticut Valley. 199 



Art. XVII.— On the Trap Tuff, or Volcanic Grit of 



If 



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by Rev. Edward Hitchcock, President of Amherst College. 



(Read before the Association of American Geologists and Naturalists in Wash- 

 ington, May, 1844.) 



In my Reports on the Geology of Massachusetts, I have given 

 a brief account of a rock under the name of tufaceous conglom- 

 erate, connected with the sandstone and trap of the Connecticut 

 valley, which appears to me to deserve more attention. For if 

 I mistake not, we have in its history, a clue that will conduct to 

 the solution of some difficult questions concerning the relative 

 age of the trap and sandstone, and the period of the elevation of 

 the latter. I have, therefore, given this rock a reexamination in 

 that part of the valley within the state of Massachusetts, and 

 propose to present the result in this paper. 



I understand all tufas of igneous origin, to have resulted from 

 fragments of scoriae and pumice, with dust from the same, falling 

 upon the dry land, or into the sea, when thrown up by volcanic 

 eruption. Sometimes they carry along with them fragments of 

 other rocks, and when they fall upon the bottom of the sea they 



mix with the sand and gravel there, and it may be that melted 



matter from the same eruption mixes with the tufaceous matter, 

 so that rocks of every grade are produced, from perfect trap to 

 stratified sandstones and conglomerates containing a portion of 

 volcanic matter and altered by heat. Such an origin and such a 

 composition correspond with the rocks which I am about to de- 

 scribe. I have observed in them the following varieties. 



Lithological Characters. 



1- -4 hard reddish micaceous sandstone, with more or less of 

 volcanic matter, mostly dust or scoria?. It is more or less meta- 

 morphic, often abounds in greenish spots, and passes insensibly 

 mto pure sandstone. 



2 - Conglomerates. — There are several varieties. The most 

 common consists of rounded masses of trap, and occasional masses 

 of red and grey sandstone, imbedded in a scoriaceous base. The 

 modules vary in size from that of a pea to masses two feet in diame- 

 ter - The trap nodules are chiefly a fine grained greenstone. They 

 ^c usually more or less rounded, but do not appear like the smooth 

 Pebbles in conglomerates of an entirely aqueous origin. They 

 have evidently^been worn mechanically, but their surfaces have 

 be en acted upon by heat, so as to have lost their smoothness. 



Other varieties take into their composition, in addition to the 

 tra P nodules, distinctly rounded pebbles of older rocks, such as 



