284 VAN HISE—METAMORPHISM OF ROCKS AND ROCK FLOWAGE. 
minus; the average of the volume reaction is plus. It has already been 
(pages 279, 280) seen that the amount of energy required for this volume 
change rapidly increases with depth, and in the lower zone it is thought 
that the plus resulting from the volume change is greater than the minus 
coming from the chemical reaction, and therefore that the residual is plus. 
Hence we conclude that the changes which take place in each of the 
zones are under the general law of the running down of energy into the 
form of heat which is dissipated, and thus accords with the apparent 
rule of the universe. 
As acorollary to the foregoing pages is the conclusion that in the upper 
zone, where pressure is relatively unimportant, upon the average, altera- _ 
_tions result in the expansion of the volume of the rocks; and in the 
deeper seated zone, where pressure is important or dominant, upon the 
average the alterations result in the contraction of the volume of the rocks. 
It follows as a further conclusion from this that the tendency of the alter- 
ations in the first zone is, upon the average, to produce minerals of lower 
specific gravity than the original minerals, while in the deeper seated 
zone the tendency upon the average is to produce minerals of higher 
specific gravity. ; 
As illustrating the first rule are the minerals produced by the disin- 
tegration and decomposition of rocks near the surface, out of which the 
sedimentary rocks are built. Some of these are kaolinite (G., 2.6—2.63), 
quartz (G., 2.65), calcite (G., 2.72), chlorite (G., 2.65-2.97), serpentine 
(G., 2.5-2.65), tale (G.,.2.7—2.8), zeolite (G., 2-2.4), limonite (G., 3.5-3.96), 
etcetera. All of these minerals and the most of the other abundant un- 
decomposed minerals, such as feldspar (G., 2.55-2.75), which make up 
great masses of sedimentary rocks, have comparatively low specific 
gravities. 
The second rule is illustrated by the change from low to high specific 
gravity of the minerals, where the sedimentary rocks are metamorphosed. 
As just seen, the minerals which compose the unaltered sedimentary rocks 
are originally those of low specific gravity. Some of the abundant re- 
sultant minerals in the equivalent metamorphosed rocks have consid- 
erably higher specific gravities, as, for instance, muscovite (G., 2.76—-8), 
biotite (G., 2.7-3.1), pyroxene (G., 3.2-3.6), and amphibole (G., 2.9-3.4), 
and the still heavier minerals, garnet (G., 3.15-4.3), staurolite (G., 3.65— 
3.75), chloritoid (G., 3.52-3.57), hematite (G., 4.9-5.3), and magnetite 
(G., 5.168-5.180). Less common heavy minerals are andalusite (G., 
3.16-8.2), fibrolite (G., 3.23-3.24), and chondrodite (G., 3.118-3.24). 
With the above are the lighter minerals, quartz and feldspar; but even 
these are quite as heavy as the average of the original minerals. 
It is noticeable that in the altered rocks in proportion as deep-seated 
