The Monoclinic. Pyroxenes of Neio York State. 177 



methods, under great pressure and high temperature no doubt, as 

 has been done artificially. 



In some cases the effect of the igenous rock seems to be to 

 cause a molecular rearrangement in the limestone, resulting in the 

 formation of new minerals by segregation. Thermal metamor- 

 phism does not seem to involve any alteration in the bulk of the 

 rock affected. Whatever part water plays, it does not act as a 

 medium in the transfer of material, and it is also probable that 

 the transportation is confined within narrow limits (A. Harker — 

 The Migration of Material During the Metamorphism of Rock 

 Masses, Jour. Geol. I, p. 574). 



The ophicalcites of the eastern Adirondacks furnish an excel- 

 lent example of the mode of formation of pyroxene by segrega- 

 tion resulting from the intrusion of the gabbros (Ref. 26). These 

 ophicalcites contain great masses of silicates, which have been 

 distorted by the violent dynamic metamorphism which the rock 

 has been subjected to. They also indicate the flowing of the 

 limestone under pressure. These limestones were originally mag- 

 nesian limestones containing great quantities of impurities, which 

 have segregated to form the pyroxenes and other silicates. These 

 silicates often form masses 23-30 feet thick. 



In support of the theory that the pyroxene results from a 

 magnesian limestone. Prof. Kemp gives the following two an- 

 alyses made by the writer, the first that of pieces of the white 

 limestone at Port Henry, which were free from silicates and the 

 second analysis, that of the white pyroxene occurring in it. 



Limestone. Pyroxene. 



SiOs 54.57 



AlA l-"^2 1.32 



FeA 



FeO 1.62 



CaO 46.79 23.23 



MgO 5.10 17.78 



K2O .70 



Na,0 .32^ 



Ufi 42.42 



96.03 99.54 



From the above analyses it will be seen that the bases and 

 silica have collected to form the pyroxene. 



The common occurrence of white pyroxene in the metamor- 



