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T. 8. Hunt on Lithology. 183 
TV. Locat MeramMorpHism. 
& 
. 
blende, chlorite, and in many cases garnet, epidote, and other 
b 
place many of these silicated minerals may be generated by chem- 
ical reactions which take place among t 
metamorphism, and in the case of the local alteration of rocks 
Y igneous masses, it is easy by comparative examinations to 
trace the chemical changes involved in the production of silicated 
minerals by the second method. In this way, Delesse has shown 
that in several cases, where the chalk of Ireland has been altered 
by the proximity of intrusive traps, the sand and clay which the 
former contains have been converted into calcareous silicates. 
Jected to the action of dilute nitric acid, and gave an insoluble 
: ge 5 
_ Tesidue with the composition u. The more thoroughly altered 
. green is h ~~ 
limestone was also treated with dilute nitric acid, which 
