CHAPTER X. 



THE AMPHIBOLITES DESCRIBED IN THE PRECEDING 



CHAPTERS. 



ANALTSES AISTD SECTIOJSTS. 



I have iu the preceding chapters described a great variety of amphibo- 

 lites, and have assigned most of them with more or less confidence to, the 

 Hst of altered sedimentary rocks. Forms which are associated with basic 

 eruptive rocks or retain any traces of the structure of those rocks I have 

 classed with eruptive rocks. Varieties which form selvages to limestone 

 beds, or are in every way closely associated with limestones and inter- 

 bedded with the schists in which they occur, I have considered to be 

 derivatives from impure limestones. Without recapitulation, I may call 

 attention to the discussion of the amphibolites associated witli Algonkian 

 limestones, on pages 29-30, and of tlie origin of the Chester amphibolite, 

 on pages 147-155, and to the description of the amphibolites of the Hawley 

 series, on pages 166-169, and of those more certainly derived from lime- 

 stones in the Conway schist, on pages 189-196, and in the BernardvSton 

 series, on pages 275-282, 290-294, 297. I bring together here for com- 

 parison all the analyses of amphibolites from the region, and a series of 

 sections commencing with forms which are certainly sedimentary and end- 

 ing with those concerning whose origin there will be difference of opinion. 

 A curious porphyritic structure which is common in the amphibolites is also 

 briefly discussed. 



I have described man^' beds of amphibolite that may, ^'^'ith more or 

 less certainty, be derived from limestone. I have perhaps given too much 

 weight to this mode of derivation, and may have included beds of igneous 

 origin. It is very striking how small the chemical variation is in rocks 

 differing widely in age, habit, and probable origin, and the close agreement 

 of all these analyses with that of an average disbase will not escape atten- 



