448 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



is used — and then cautiously — for identifying equivalent beds. Has any 

 one i^roved by careful observation that crystals of staurolite, cyanite, or andalu- 

 site, are restricted to rocks of a certain geological period ? Assumptions and 

 opinions, however strongly emphasized, are not proofs. It is no objection to 

 stratigraphical evidence that it is difficult to obtain ; is very doubtful on ac- 

 count of the difficulties ; may take scores of years in New England to reach 

 any safe conclusions. It must be obtained, whatever labor and care it costs, 

 before the real order and relations of the rocks can be known. Until then, 

 lithology may give us guesses, but nothing more substantial. Mr. Hunt's 

 arguments with reference to the White Mountain Series, as urged by him in 

 1870, will be found in this journal, II, L, 83. Both there, and in his ad- 

 dress, may be seen the kind of evidence with which he fortifies, or sup- 

 plements, that based on the character of the rocks. Direct stratigraphical 

 investigation over the region itself, in which all flexures, faults, and uncon- 

 foriuabilities have been thoroughly investigated, is not among the foundations 

 of opinion which he brings forward. He endeavors to set aside the objection 

 to his views suggested by the existence of Devonian or Helderberg rocks in 

 central and northern New England ; but he present.s, for this purpose, only 

 some general considerations, of little weight, instead of definite facts as to the 

 extent and variety of metamorphic strata that are part of, because conformable 

 to, these Helderberg beds. Had he studied up these stratigraphical relations 

 with the care ret^uisite to obtain the truth, and all the truth, perhaps he would 

 not longer say — it is ' contrary to my notions of the geological history of the 

 continent to suppose that rocks of Devonian age could in that region have 

 assumed such lithological characters.' Notions often lead astray." (See also 

 Am. Jour. Sci., 1871, (3) II., pp. 205-207; 1872, IV., pp. 104, 105.) 



In replying to Professor Dana, Dr. Hunt states (Amer. Jour. Sci., 

 1872, (3) IV., p. 51): — 



" With regard to New England rocks. Prof. Dana asserts that ' there are 

 gneisses, mica schists, and chloritic and talcoid schists in the Taconic series.' 

 I have, however, shown in my address that Emmons, the author of the Taconic 

 system, expressly excluded therefrom the crystalline rocks, which he included 

 in an ohler primary system ; excepting, however, certain micaceous and tal- 

 cose beds, which he declared to be recomposed rocks, made up from the ruins 

 of the primary schists, and distinguished from these by the absence of the 

 characteristic crystalline minerals which belong to the Green Mountain i)ri- 

 mary schists. Again, Prof. Dana states that I make the crystalline schists 

 of the White Mountains a newer series than the Green Mountain rocks. A 

 careful perusal of my address will show that I nowhere assert that the rocks of 

 the third series, on my line of section, are younger than the second series. 

 Such a view of their relations has, however, been maintained for the last 

 generation by the Messrs. Rogers, Logan, and many others, all of whom 

 assigiieil the crystalline schists of the White Mountains to a higher geological 

 horizon than the Green Mountains My ' chronological arrangement ' of 



