364 A TREATISE ON METAMORPHISM'. 



2.54 to 2.76); (2) pyroxene group (sp. gr. 2.68 to 3.58); (3) amphibole 

 group (sp. gr. 2.9 to 3.713); (4) garnet group (sp. gr. 3.41 to 4.30); (5) chrys- 

 olite group (sp. gr. 3.2 to 4.1); (6) scapolite group (sp. gr. 2.566 to 2.74); 

 (7) aluminum silicate group (sp. gr. 3.16 to 3.67); (8) humite group (sp. gr. 

 3.1 to 3.2); (9) tourmaline (sp. gr. 3.09); (10) staurolite (sp. gr. 3.71); (11) 

 mica group (sp. gr. 2.7 to 3.1); (12) clintonite group (sp. gr. 2.9 to 3.57). 



The average specific gravity of the mineral groups above mentioned 

 as products of the zone of katamorphism is 2.948. The average specific 

 gravity of the mineral groups- of the zone of anamorphism is 3.488. It 

 thus appears that the average specific gravity of the minerals which develop 

 in the zone of anamorphism is 18 per cent greater than that of the 

 minerals in the zone of katamorphism. This comparison is of course very 

 roughly approximate, since the various minerals are not present in equal 

 quantities. Probably the percentage is too great, since the heavy sulphides 

 and the very heavy silicates are given equal weight with the abundant but 

 lighter quartz, feldspars, pyroxenes, amphiboles, and micas. The com- 

 parison, however, shows beyond question that a given mass of material 

 occupies much less space in the lower physical-chemical zone than in the 

 upper physical-chemical zone. 



It is shown under the next heading that many of the reactions written 

 for the minerals of the zone of katamorphism may be read in reverse order 

 when the resultant minerals are buried so deep as to be in the zone of 

 anamorphism. The lighter minerals characteristic of the zone of kata- 

 morphism reunite to produce heavier minerals of the zone of anamorphism, 

 such as the feldspars, the micas, the pyroxenes, the amphiboles, the chryso- 

 lites, andalusite, etc. Furthermore, where the pressure is great enough 

 these minerals rearrange themselves again in whole or in part so as to 

 produce still heavier minerals, such as garnet, staurolite, tourmaline, 

 sillimanite, cyanite, etc. This great change takes place within the narrow 

 range of less than 10,000 meters. 



Since in this mere outer film of the earth a great diminution in the 

 volume of the minerals has taken place, it is thought to be highly probable 

 that, even if the average chemical composition of the interior of the earth 

 be supposed to be the same as the crust, the pressure is such that the min- 

 erals mav further rearrange themselves into still more compact products, 

 thus probably producing minerals of a different kind and higher specific 



