KINDS OF ROCKS. 435 
3. The Mica and Scda-lime-Feldspar series. These grani- 
toid rocks are equally alkali-yielding with those of the true 
granite group, but the alkali is mainly soda. The nephelite 
(clezolite) rocks not hornblendie are here included, although 
they contain in general some microline or orthoclase. 
4. The Hornblende and Potash- -Feldspar series, or the Sye- 
nyte group. In this series, the mica of the oranite series 1s 
replaced by the non-alkaline mineral, hornblende. Transi- 
tions between the granite and syenyte rocks are common—a 
bed that is true mica schist often becoming hornblendic ; 
the same specimen may have mica and hornblende crystals 
together, or parallel mica and hornblende layers, and then 
not far beyond the schist may be a purely hornblende rock ; 
and so there are similar transitions in other parts of the 
two series. ‘This transition in a stratum of mica schist, a 
metamorphic rock, indicates merely that the mud-bed or 
sedimentary stratum, out of which the mica schist was 
made, had a diminished proportion of alkali in some parts, 
and, in still others, a complete absence of alkali—which 1s 
just such a variation as might be looked for in oceanic sedi- 
ments, as they spread over a wide region. ‘The hornblende 
may be replaced by epidote, another iron-bearing mineral. 
9. The Hornblende and Soda-lime-Feldspar series. ‘The 
soda-lime-feldspars, in this series, may be either of the 
triclinic species, from albite to anorthite. | 
6. The Pyroxene and Soda-lime-Feldspar series. The soda- 
lime-feldspars are the same as in the preceding. Quartz 
is very rarely present, except in traces. Potash replaces 
soda in amphigenyte. 
7. Pyroxene, Garnet, Epidote and Chrysolite rocks, con- 
taining little or no Feldspar. 
8. Hydrous Magnesian and Aluminous rocks. 
9. Iron Ore rocks. 
1. SILICEOUS ROCKS. 
1. Quartzyte, Granular Quartz.—A siliceous sandstone, 
usually very firm, occurring in regions of metamorphic 
rocks. It does not differ essentially from the harder sili- 
ceous sandstones of other regions. Conglomerate beds are 
sometimes included. 
VARIETIES.—a. Massive. b. Schistose. oc. Calearcous; sometimes 
contains disseminated calcite which, where the rock is exposed 1o 
‘weathering, is removed and leaves the rock loose in texture, or celiu- 
