IMPORTANCE OF WATER IN RECRYSTALL1ZAT10N. 743 



tionecl the schists and gneisses of the Basement Complex of the Marquette 

 district of Michigan. Two analyses of the Kitchi schists showed, respec- 

 tively, 2.51 and 2.70 per cent of water above 100° C.° A micaceous schist 

 gave off 2.04 per cent of water above 100° C. b A Palmer gneiss gave off 

 2.33 per cent of water above 100° C. c Partial analyses of two other 

 micaceous schists from the same locality as the micaceous schist above 

 referred to, which show a cataclastic or granulated structure, unfortunately 

 do not include water determinations. 



The foregoing analyses of recrystallized schists from the Archean and 

 Algonkian may be taken as typical of the recrystallized schists of all ages 

 the world over. This is shown to be evident by running through the 

 various analyses of the recrystallized schists in any of the published tables 

 of analyses. Such tables show that the recrystallized schists average more, 

 rather than less, than 1.50 per cent of combined water, and in many cases 

 that they contain more than 2 per cent of water. 



In Clarke and Hillebrand's book of analyses/' besides those mentioned, 

 are found three other analyses of recrystallized gneisses. The analyses are 

 of typical gneiss, derived from basic granite at Washington, D. C, with a 

 water content (at and above 110° C.) of 1.97 per cent, and two plagioelase 

 gneisses from the Sierra Nevada, with a water content (at and above 

 110° C.) of 1.71 and 1.47 per cent, respectively. These analyses, with 

 those already quoted, cover all the schists and gneisses cited in Clarke and 

 Hillebrand's book which, from the available descriptions, can be ascertained 

 to be certainly recrystallized. They are here included to show that in this 

 bulletin there is no exception to the rule laid down, viz, that when rocks are 

 deformed in the zone of anamorphism, which contain a sufficient amount of 

 combined water to serve for recrystallization, this process is dominant rather 

 than granulation. 



It is to be noted that the water contents of the schists and gneisses 

 mentioned are amounts given off above 100° C, and in most cases above 

 110° C; in other words, the water is combined water. This point is of 

 importance as showing that, after the metamorphism of the rocks to schists 



"Van Hise, C. R., and Bayley, W. S., The Marquette iron-bearing district of Michigan: Mon. II. S. 

 Geol. Survey, vol. 28, 1897, p. 168. 



&Mon. 28, cit,, p. 202, anal. vi. 



«Mon. 28, cit., p. 217. 



d Clarke, F. W., and Hillebrand, W. F., Analyses of rocks and analytical methods: Bull. U. S. 

 Geol. Survey, No. 148, 1897, pp. 88, 215. 



