G. II. WILLIAMS — OBSERVATIONS IN NORWAY. 553 



cious and highly magnesian limestone would not require a great addition of material 

 to change it into an aggregate of garnet and diopside. As regards the basic rocks, I 

 cannot speak with as much certainty of the Norwegian occurrences as of other rocks 

 of a similar character in the neighborhood of Baltimore, where like changes have 

 been produced by regional metamorphism. Here the resulting products, composed of 

 feldspar and hornblende, do not in any particular differ in chemical composition from 

 the original rock, composed of pyroxene and feldspar. 



Professor B. K. Emerson: I desire to add a word, partly from interest in the 

 speaker and in recognition of the admirable way in which the matter has been pre- 

 sented by him, and partly from reminiscences that came up of travel many years ago 

 in the region he has described. This discussion of regional metamorphism brought 

 to my mind the work of President Hitchcock upon the same subject, and especially 

 his work on the fossiliferous Devonian schists at Bernardston, Massachusetts. On 

 examining a large series of these Bergen specimens with Professor Rosenbusch a few 

 years ago, I found that the Bernardston Devonian locality described so long ago by 

 President Hitchcock and Professor Dana affords representatives of all, or the major 

 portion of those rocks — quartzite with all the pebbles rolled out and cut sharp by 

 faulting and jointing, hornblende schists in every variety except those which seem to 

 have come from the- metamorphism of eruptive rocks (that is, hornblende schists 

 that seem to come from the metamorphism of limestone but show no trace of tufa or 

 volcanic origin), beds of the most compact and pure magnetite with fossils immedi- 

 ately above and below them, and these fossils in highly crystalline limestone cut 

 through by granite veins and in mica-schists piece for piece like those taken from 

 Bergen. These things, like the facts of history, have to be re-described and re-written, 

 and come at last to be believed. Of course the work of President Hitchcock was done 

 without the aid of the microscope, and it was pushed far beyond the limits of the 

 field at Bernardston. 



I was surprised in passing recently one of the college buildings at Amherst which 

 is built of gneiss to see that several of the blocks showed the altered pebbles of the 

 conglomerate of which the rock was made. This is the so-called Munson granite 

 that stretches across the state east of Amherst; and that same conglomerate granite 

 wraps around the Archean of the western part of the state and forms there a coarse 

 shore deposit. This granitoid gneiss was supposed by President Hitchcock to be the 

 last term of the metamorphism of a conglomerate. It seems to me that the distinc- 

 tion between the regional metamorphism and the metamorphism caused by manifest 

 contact of eruptive rock, where the two effects are superimposed, will be found in the 

 introduction in the latter case of chemical materials that have been brought up with 

 the eruptive rocks. Any contacts which show, as those I have studied in Massachu- 

 setts, the presence of minerals containing boracic acid and a large increment of alka- 

 lies, as compared with the same bed more removed from the intrusive rock, enable 

 one at times to distinguish quite clearly between the regional and the contact effects. 

 This is especially clear with aluminous sediments when the normal metamorphism 

 develops chiastolite, ottrelite, staurolite, garnet, graphite. The contact influence of 

 the eruptive adds coarse muscovitc in abundance, feldspars, tourmaline, cordierite, and 

 suppresses (resorbs) for the most part the purely aluminous silicates of the first group, 

 though their former presence may be noted by their pscudomorphs in muscovitc. 



