552 PROCEEDINGS OF NEW YORK MEETING. 



granite is coarse below but rapidly becomes Bner grained toward the contact, and is 

 almost cryptocrystalline along the edge of the sedimentary beds. The thick cover- 

 ing of Silurian strata is continuous over the entire mass, their dip following the con- 

 tact, even down the Bteep eastern Blope. The metamorphism of these overlying beds 

 is plainly due to the granite, and anastomosing dikes of the latter rock penetrate them 

 vertically, but without reaching the present surface. 



On leaving the Christiania region for the western coast of Norway, the opportu- 

 nity was enjoyed of examining the regionally metamorphosed eruptive and sedimen- 

 tary rocks near Bergen, under the guidance of Professor Bans Reusch, whose well- 

 known works* on the geology of this district have given it a world-wide fame. The 

 remarkable mica-schists of Vagtdalen were visited, containing, in spite of their highly 

 crystalline character, well preserved remains of trilobites and orals. Moreover, 

 where the metamorphism has completely destroyed the fossils in the Bchists, they are 

 often preserved in intercalated calcareous lenses. (Specimens of all these rocks were 

 exhibited to the Society.) 



Much more of importance in its bearing upon regional or dynamic metamorphism 

 was seen near Bergen and on the island of Bemmelo, further to the south. Time, 

 however, forbids the further entering into detail; but the series of specimens will 

 serve. Letter than words, to illustrate to those who are interested in the subject, what 

 are the most striking facts. 



Suffice it, in conclusion, to indicate certain points which seem capable of general 

 application to metamorphic rocks, and to the truth of which these observations in 

 Norway offer strong corroborative testimony: 



1. The mint ralogical changes produced in a given rock by both contact and dynamic 

 metamorphism are in general similar, while the structural alterations brought about 

 bv the .-aine agencies are usually in striking contrast. In tic case of the basic erup- 

 tives above mentioned the paramorphism of pyroxene to hornblende is accomplished 

 either within the contact zone of syenite or by orographic pressure; although it is 

 only bv the latter mean- that the rock is converted into a schist by the- development 



of foliation. 



2, [f the action of dynamic metamorphism i- carried far enough it is capable of 

 producing the Bame result from rocks originally most distinct in character and origin. 

 An eruptive ma-- and a sediment, if sufficiently alike in chemical composition, may, 

 when subjected to intense pressure, develop into foliated rock- whi< h cannot be dis- 

 tinguished. It i-, therefore, | ible to trace out the origin of the crystalline schi 



only .up to a certain point. We may separate those which are igi us from lie 



which are (da-tic, bo long a- any distinctive characters remain ; but if, as is very often 

 the case, the original structure has been obliterated by metamorphism, such a Bepara 

 lion becomes hopeli 



Professor J. S. Newberry: 1 would ask Professor William- to add a Bingle fact 

 to the very clear and interesting exposition he has given to us. How far has there 

 been, in these different cases, substitution or transfer of material? I would ask it 

 he ha- the chemical < Btitution of the unaltered and tic altered rocks to compare. 



p -v Williams: This differs very much in different cases. Bere we havea 



limestone transformed into an aggregate of garnet and pyroxene; this mean- a very 

 considerable substitution. Some limestones are, however, silicious : and a highly siti- 



Isted mi.. German 

 v i Ingliah BUtnm urv "i • lenl 



