CHAPTER XIII. 

 TRIASSIC ERUPTIVE ROCKS. 



HISTORICAIi. ' 



As early as 1815 President Hitchcock described the "Basal tick Col- 

 umns" of Titan's Piazza in the first volume of the North American Review.^ 

 He gave the "greenstone" only a word in the Geology of Deerfield,- not 

 distinguishing it from the hornblende-schist of West Northfield. It is 

 described at some length in the Geology of the Connecticut'' as "secondary 

 greenstone," -without reference to its mineralogical constitution. He notes 

 that it is more amygdaloidal in its tipper portion, describes the contact of 

 the upper sandstone on the trap in Sunderland and Deerfield, and interprets 

 the fault at the mouth of Fall River, described below (p. 437), as a repe- 

 tition of the trap. 



In his earher report upon the Geology of Massachusetts* he gives a 

 very full account of the "greenstone," touching upon its lithological pecul- 

 iarities, its distribution, mineral contents, and origin, an account which has 

 lost little of its value, and which, because of its great length, I shall only 

 briefly summarize here, as the main points are cited beyond. He now 

 considers the "greenstone" to be made up of feldspar and hornblende, and 

 remarks that he has not met with a genuine and distinct dike of trap in 

 the sandstone. 



In the later edition of the above work (1835), and in the Final Report,^ 

 the same account is reprinted almost verbatim, the only additional informa- 

 tion given relating to the small dikes in the gneiss on the east of the sand- 

 stones. An inspection of the maps accompanying the above reports shows 

 clearly that the trap was laid down most accurately on the map of 1823, 



' Pase 337. 



■Am. Jour. Sci., Ist series, Vol. I, 1819, p. 105. 



'Am. Jour. Sci , Ist series. Vol. VI, 1823, p. 44. 



'Geol. of Mass., Amherst, 1833, p. 404. 



6Geol. of Mass.. Final Kept., Amherst, 1841, p. 640. 



407 



