Gh. XXVI.] 
CALLED c PRIMARY.' 
367 
strata of pure siliceous sand alternating with micaceous sand 
and with layers of clay, so in the ' primary' we have beds of 
pure quartz rock alternating with mica-schist and clay-slate. 
As in the secondary and tertiary series we meet with limestone 
alternating again and again with micaceous or argillaceous sand, 
so we find in the f primary' gneiss and mica-schist alternating 
with pure and impure granular limestones. 
Passage of gneiss into granite — If, then,, reasoning from the 
principle that like effects have like causes, we attribute the 
stratification of gneiss, mica-schist, and other associated rocks, 
to sedimentary deposition from a fluid, we encounter this diffi- 
culty, that there is often a transition from gneiss, one of the 
stratified series, into granite, which, as we have shown, is of 
igneous origin. Gneiss is composed of the same ingredients as 
granite, and its texture is equally crystalline. It sometimes 
occurs in thick beds, and in these the rock is often quite 
undistinguishable, in hand specimens, from granite; yet the 
lines of stratification are still evident. These lines imply depo- 
sition from water, while the passage into granite would lead us 
to infer an igneous origin. In what manner can we reconcile 
these apparently conflicting views ? The Huttonian hypothesis 
offers, we think, the only satisfactory solution of this problem. 
According to that theory, the materials of gneiss were originally 
deposited from water in the usual form of aqueous strata, but 
these strata were subsequently altered by their proximity to 
granite, and to other plutonic masses in a state of fusion, until 
they assumed a granitiform texture. The reader will be pre- 
pared, by what we have said of granite, to conclude, that when 
voluminous masses of melted rock have been for ages in an 
incandescent state, in contact with sedimentary deposits, they 
must produce some alteration in their texture, and this alteration 
may admit of every intermediate gradation between that result- 
ing from perfect fusion, and the slightest modification which 
heat can produce. 
The geologist has been conducted, step by step, to this 
