140 Barrell — Groivth of Knowledge of Earth Structure. 



Origin of Greenstone. 



Does the greenstone of the Connecticut afford evidence in 

 favour of the Wernerian or of the Huttonian theory of its 

 origin? Averse as 1 feel to taking a side in this controversy, I 

 cannot but say, that the man who maintains, in its length and 

 breadth, the original hypothesis of Werner in regard to the 

 aqueous deposition of trap, will find it for his interest, if he 

 wishes to keep clear of doubts, not to follow the example of 

 D'Aubuisson, by going forth to examine the greenstone of this 

 region, lest, like that geologist, he should be compelled, not only 

 to abandon his theory, but to write a book against it. Indeed, 

 when surveying particular portions of this rock, I have some- 

 times thought Bakewell did not much exaggerate when he said 

 in regard to Werner's hypothesis, that, 'it is hardly possible 

 for the human mind to invent a system more repugnant to 

 existing facts.' 



On the other hand, the Huttonian would, doubtless have his 

 heart gladdened, and his faith strengthened by a survey of the 

 greater part of this rock. As he looked at the dikes of the old 

 red sandstone, he would almost see the melted rock forcing its 

 way through the fissures ; and when he came to the amygdaloi- 

 dal, especially to that variety which resembles lava, he might 

 even be tempted to apply his thermometer to it, in the suspicion 

 that it was not yet quite cool ... (p. 59). 



By treating the subject in this manner I mean no disrespect 

 to any of the distinguished men who have adopted either side of 

 this question. To President Cooper especially, who regards the 

 greenstone of the Connecticut as volcanic, I feel much indebted 

 for the great mass of facts he has collected on the subject. And 

 were I to adopt any hypothesis in regard to the origin of our 

 greenstone, it would be one not much different from his" (p. 60) . 



By 1833 and more clearly in 1841 Hitchcock had come 

 to recognize the distinction between intrusive and extru- 

 sive basaltic sheets in the Connecticut valley. Dawson 

 also came to regard the Acadian sheets as extrusive, and 

 Emerson in 1882 recalled again the evidence for Massa- 

 chusetts (24, 195, 1882). Davis, however, went a step 

 further and by applying distinctive criteria not only sep- 

 arated intrusive and extrusive sheets throughout the 

 whole Triassic area, but by using basalt flows as strati- 

 graphic horizons unraveled for the first time the system 

 of faults which cut the Triassic system. His preliminary 

 paper (24, 345, 1882) was followed by many others. 



From 1880 onward begins the period of precise struc- 

 tural field work. The older geologists mostly conceived 

 their work after reconnaissance methods. From 1870 to 



