6 9 



During the change of No. I into No. 2 and this into 

 No. 3, the information afforded by the analyses bears out 

 that obtained from the study of the thin sections, showing 

 that there has been a very considerable rearrangement 

 among the constituents of the rock. Thus it is seen that 

 while the alumina and alkalies increase in No. 2 and N0.3 

 there is not a corresponding increase in the total amount 

 of silica; the silica required to make additional feldspathic 

 constituents is derived from some other reactions going 

 forward in the rock. 



It seems also that after the development of a certain 

 percentage of silicates in the limestone, as shown in No. 1, 

 during which process carbonic acid was expelled and the 

 lime combined with it used in the production of new 

 minerals, no further lime was fixed. In the earlier stages 

 the waters given off by the granite having accomplished 

 the transference of material in the limestone, passed off 

 with the replaced CO2 in solution, leaving the lime behind. 

 In the later stages of the alteration, however, these waters 

 while continuing to deposit silicates in the limestone, made 

 place for them by carrying off carbonate of lime in 

 solution. 



As will be seen, the difference in chemical composition 

 between Specimen 2 and Specimen 3 is very small. The 

 more highly altered rock, No. 3, is rather richer in iron, 

 magnesia, and alkalies, while it is considerably poorer in 

 lime and contains less chlorine. These difference are seen 

 to represent a slight increase in the proportion of horn- 

 blende and orthoclase present and a decrease in the amount 

 of plagioclase and scapolite in the rock. 



If, for the purpose of comparing the composition of 

 these alteration products with that of igneous rocks, the 

 norms are calculated, these are found to be as follows. 

 Since No. 3 is essentially the same as No. 2, the norm of the 

 latter rock may be taken to represent both specimens and 

 with it is given the norm of the silicated portion of No. 1 

 (No. 1 (b)). 



