^^ 



40 



BULLETIN OF THE 



seen to be composed of plagioclase, a little orthoclasc, augite, olivine, 

 magnetite, hematite, viridite, ^nd apatite. The feldspar encloses bits 

 of the original base, part of which is now devitrified, bnt part remains as 

 an unchanged globnlitic base. This affords additional proof that the 

 diabases are simply old crystalline basalts. Tlio augitc is quite clear 

 and unaltered except in some places. The olivine is considerably 

 changed, yet the centre frequently shows the unchanged mineral. 

 These olivines, like those in modern basalts, are in fragments, grains, 

 and rounded and penetrated crystals, showing in this way their prior 

 origin to the crystallization of the rock in situ. 



In the sketch of the literature given before, it is seen that Messrs. 

 Kivot, Kimball, Hunt, Winchell, Credner, Brooks, and Wright regard the 

 so-called "diorites" as sedimentary rocks, metamorphosed in situ, and in 

 general teach that they gradually pass into the schists on cither side; 

 i. e. they form one and the same inseparable series of sedimentary 

 deposits. This passage, by insensible gradations, it is said, was estab- 

 lished by the field observations of all except Dr. T. Stcrry Hunt, who, it 

 seems, based his conclusions upon lithological evidence ; for we fail to 

 find the slightest evidence in his writings that he had any personal 

 acquaintance with the district. On the other hand, Messrs. Foster and 

 Whitney taught that these rocks were intrusive, basing their conclusions 

 upon their observations in the field. 



Special pains were taken by us in the field to see which of the two 

 views were correct. Where the conditions were such in the field that 

 any evidence could be obtained bearing on cither side, that evidence was 

 always of the positive kind, and sustained Messrs. Foster and Whitney. 

 The evidence of the six observers quoted on the opposite side was of the 

 negative kind ; i. e. they could not or did not see any distinct junc- 

 tion between the two rocks ; tlierefore it was assumed that none existed. 

 Where the contacts were covered, or broken and obliterated by frost 

 and atmospheric agencies, the proof on cither side is nil ; but when 

 such is not the case, and we have on one side '' dioritc " and on the other 

 schist, the question is. Do they or do they not pass into each other 1 

 Both rocks are of a greenish hue generally, and to the eye untrained 

 to observe the minutest changes and differences in rocks, they look 

 alike. It is therefore to be expected that the •majority, at least, of ob- 

 tiervcrs will walk directly over the junction between two rocks, especially 

 if they believe in the prevailing theories, and declare tliat they pass 

 directly into each other by insensible gradations. The only tiling such 

 negative evidence gives in this case is the proof that either the observer 



