Formation of Continents and Oceanie depressions. 
rocks: made up of augite and labradorite, with sometimes 
anorthite or oligoclase, often chrysolite, and generally magne- 
tite in disseminated grains, and varying in specific gravity 
mostly between 2°8 and 3:2. : 
The acidic comprise (1) most trachyte and related feldspathic 
rocks, consisting of one or more of the feldspars, oligoclase, 
albite, or orthoclase, with usually a little hornblende and mag- 
netite, and sometimes mica, and not unfrequently free quartz— 
Sp. gr.=25-2-75; (2) syenite, consisting of orthoclase and 
hornblende with quartz—sp. gr.=2°9-3:1; hyposyenite, con- 
sisting of orthoclase and hornblende without quartz—sp. gt. — 
9-3-2 :+ diorite, consisting chiefly of oligoclase or albite with 
hormblende—sp. gr.=2°80-8°1; granite, consisting of ortho- 
mica—sp. gr.=2°6-2°75. 
(c.) These igneous rocks are also conveniently arranged with 
reference to their origin into an dron-bearing and a compara- 
tively tron-free series. 
* Bull. Soc. Geol. de France, II, iv, 1253, 1847. De la Beche has the idea in 
it in his his Geological Researches (1834). Bunsen uses 
it in his memoir on the volcanic rocks of Iceland (Pogg., Ixxxiii, 201, 1851), and 
, quartz-bearing rock, as 
it was described from the locality Syene in Egypt, where that kind occurs; ry 
free from quartz 1 ad 
therefore, call the kind hupeyenite. Syenite is a rock of 
hornblendic series in all its sestaieion relations, it graduating often into hyposy- 
a regions; and it is to make it, as done some German 
thologists, a hornblendic variety of granite. It deserves to stand as a distinct 
species, and it naturally leads off the hornblendic or syenitic series of crystalline 
Tocks, a8 granite Anaa th 1 si a: granitic series. 
