120 HOW CROPS FEED, 
Tue Syenrric SERIES 
consisting chiefly of Quartz, Feldspar, and Amphibole. 
Syenite is granite, save that amphibole takes the place 
of mica. In appearance it is like granite; its color is usu- 
ally dark gray. Syenite isa very tough and durable rock, 
often most valuable for building purposes. The famous 
Quincy granite of Massachusetts is a syenite. Syenitic 
Gneiss and Hornblende Schist correspond to common 
Gneiss and Mica Schist, hornblende taking the place of 
mica, 
Tue Votcanic SERIES 
consisting of Feldspar, Amphibole or Pyroxene, and 
Zeolites, 
Diorite is 2 compact, tough, and heavy rock, common- 
ly greenish-black, brownish-black, or grayish-black in 
color. It contains amphibole, but no pyroxene, and is 
an ancient lava. 
Dolerite or Trap in the fine-grained varieties is scarcely 
to be distinguished from Diorite by the appearance, and is 
well exhibited in the Palisades of the Hudson and the 
East and West Rocks of New Haven. It contains pyrox- 
ene in place of amphibole. 
Basalt is like dolerite, but contains grains of chrysolite. 
The recent lavas of volcanic regions are commonly basaltic 
in composition, though very light and porous in texture. 
Porphyry.—Associated with basalt occur some feld- 
spathic lavas, of which porphyry is common. It consists 
of a compact base of feldspar, with disseminated crystals 
of feldspar usually lighter in color than the mass of the 
rock. 
> Pumice is a vesicular rock, having nearly the composi- 
tion of feldspar. . 
Tue Maenesian SErRrEs 
consisting of Quartz, Feldspar and Taic, or Chlorite. 
Talcose Granite differs from common granite in the 
substitution of talc for mica. Is a fragile and more easily 
