33B 



GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



ANALYSES OF TONALITE. 



Analyses of the tonalite were made in the laboratory of Amherst 

 Colleg-e (1) by William Orr, jr., and (2) by F. H. Fitts. A third (3) was 

 made by L. G. Eakins, of the United vStates Geological Survey: 



Analyses of timaUte. 



SiO;.. 



TiOi - 

 Al.Oj. 

 Fe.Oj 

 FeC- 

 MnO . 

 BaC. 

 CaC- 

 MgO. 

 Na,0 . 

 K,0.. 

 H,0.. 

 P:0,.- 



56.69 



.62 



15.48 



6.22 



7. .59 

 6.53 

 3.41 

 3.43 



56.18 

 1.60 



6.49 

 6.53 

 3.40 

 3.27 



55.51 



.91 



16.51 



1.68 



4.57 



. 11 



.02 



6.73 



6.73 



3.19 



2.46 



1.53 



.17 



100.12 



Analyses 1 and 2 were made from tlie same hand specimen of the 

 slig-htly amethystine, fresh, medium-g-rained tonalite, which showed with 

 the lens dark, bronzy diallage, and bright-green hornblende and amethys- 

 tine (quartz. The specimen came from just north of Three Rivers, in 

 Belchertown. Analysis 3 was made from the beautiful epidotic-veined rock 

 from the crossroads east of South Leverett, described on page 339, which 

 was more altered than the others. 



PETROGRAPHICAL DESCRIPTION. 



Macroscopical. — The rock is a wlioU}' granitoid, medium- to fine-grained 

 and very even-grained mixture of quartz, orthoclase ("?), plagioclase, bit)tite, 

 and hornblende, the latter being at times replaced by a dark-bronze dial- 

 lage in the Belchertown area, a mineral which occurs very rarely in the 

 Hattield region. The passage of diallage into hornblende can be well 

 observed, and reasons will be given below for the assumption that the rock 



