CLASSIFICATION OF THE NEW HAMPSHIRE FORMATIONS. 659 



Every one will grant at the outset that onr field of labor must abound 

 in inverted flexures and dislocations of the strata. Those who are not 

 familiar with inversions will not be prepared to accept our statements at 

 the first reading of them, because they seem contradictory to nature. It 

 is only because inversions are the opposite of reality that apparently ex- 

 travagant statements are correct. One who will apply the ordinary rules 

 of superposition to the formations of a country like ours, will not only fail 

 to detect the true structure, but will involve himself in labyrinthine per- 

 plexity. If our interpretation fails in any particular it will be in the neg- 

 lect to invoke all the inversions and faults that are required for truthful 

 elucidation. 



Let us take an example for illustration. A section twenty miles long 

 crosses a formation — say a hornblende schist — four times. The strata 

 all dip in the same direction, both the hornblende rock and the interca- 

 lated groups. The natural method of interpretation is, to say there are 

 four different horizons of this formation. One who has explored much 

 among the crystallines will find it desirable to say there is but one for- 

 mation, and that has been repeated three times. That view will simplify 

 the classification, perhaps allowing us to refer the seven separate bands 

 of the section to two. Cases exactly like this can be found, but usually 

 the same bed is not repeated so many times. The principle is one that 

 we are compelled to accept as fundamental, and to apply constantly. 



Our older formations show a tendency to assume an ovoidal shape. 

 Those familiar with New England geology will recall the similar repre- 

 sentation of Percival's ancient groups in Connecticut, called K i, K 2, 

 and K 3. Our porphyritic and Bethlehem gneisses show this feature 

 the most markedly. Where no subsequent disturbances have modified 

 the natural order of the later bands, grouped concentrically around the 

 ovoid nucleus, an easy method of determining relative age is afforded, 

 even ifthe whole series is inverted. Then if there is a number of the 

 ovoidal areas, not very far apart, we understand the comparatively recent 

 origin of the rocks between them. 



Another important doctrine relates to the identification of formations 

 in our field of labor by means of mineral characters. Allowing for a 

 certain degree of modification, we must believe that the same kind of 

 rock in adjoining counties, or for greater distances, belongs to the same 



