308 VAN HISE—METAMORPHISM OF ROCKS AND ROCK FLOWAGE. 
ity as the mica-schist 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 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 typical crystalline schists. The analyses 
are of typical gneiss, derived from basic granite, city of Washington, with 
a water content, above 110° C., of 1.97 per cent, and two plagioclase- 
eneisses from the Sierra Nevada, with a water content, above 110° C., of 
1.71 and 1.47 per cent respectively. These analyses, with those already 
quoted, cover all of the schists cited in the Bulletin 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. 
It is noted in the analyses quoted that the water contents are amounts 
given off above 100° C.; in other words, the water iscombined water. This 
point is of importance as showing at the time metamorphism occurred 
that water was present in sufficient amount, so that upon an average 1.5 
per cent or more was, worked into or was already within the body of the 
minerals. These amounts of the combined water are, of course, no meas- 
ure of the amount of the water, free and combined, contained by the rock 
during the metamorphosing process. Indeed, itis highly probable that the 
amount of combined water in the later stages of the process, in the case 
at least of the sedimentary rocks, is lower than in the earlier stages of 
the process, and consequently water is continuously driven off during 
the process, thus ever renewing the water films in the subcapillary spaces 
and furnishing a medium for solution and redeposition. This may be 
illustrated by the analyses of slates and shales, and clays and soils, given 
by Clarke and Hillebrand. Twenty slates and shales from Vermont, 
Colorado, and California gave an average of 4.42 per cent of water above 
100° C. Fourteen slates and shales from Vermont, New York, Kentucky, 
Georgia, and Alabama gave an average of 4.34 percentage of water above 
110° C.F It is well known that slates and shales when profoundly meta- 
morphosed by mass dynamicaction produce mica-schists or mica-gneisses. 
* Analyses of rocks and analytical methods, U.S. Geological Survey, by F. W. Clarke and W. F . 
Hillebrand: Bull. U. 8. Geol. Survey, no. 148, 1897. 
} Loe. cit., pp. 277-286. 
