596 
ELEMENTS OF GEOLOGY. 
whether the foliation does or does not accord with that ar¬ 
rangement which gravitation, combined with current-action, 
imparted to a deposit from water. Moreover, when we look 
for stratification in crystalline rocks, we must be on our 
guard not to expect too much regularity. The occurrence 
of wedge-shaped masses, such as belong to coarse sand and 
pebbles—diagonal lamination (p. 42)—ripple-marked, uncon¬ 
form able stratification—the fantastic folds produced by later¬ 
al pressure—faults of various width—intrusive dikes of trap 
—organic bodies of diversified shapes, and other causes of 
unevenness in the planes of deposition, both on the small 
and on the large scale, will interfere with parallelism. If 
complex and enigmatical appearances did not present them¬ 
selves, it would be a serious objection to the metamorphic 
theory. Mr. Sorby has shown that the peculiar structure be¬ 
longing to ripple-marked sands, or that which is generated 
when ripples are formed during the deposition of the materi¬ 
als, is distinctly recognizable in many varieties of mica-schists 
in Scotland."^ 
In the accompanying diagram I have represented careful¬ 
ly the lamination of a coarse argillaceous schist which I ex¬ 
amined in 1830 in the Pyre¬ 
nees. In part it approaches 
in character to a green and 
blue roofing-slate, while part 
is extremely quartzose, the 
whole mass passing down¬ 
ward into micaceous schist. 
The vertical section here ex¬ 
hibited is about three feet in 
height, and the layers are 
sometimes so thin that fifty 
may be counted in the thick¬ 
ness of an inch. Some of them consist of pure quartz. There 
is a resemblance in such cases to the diagonal lamination 
which we see in sedimentary rocks, even though the layers of 
quartz and of mica, or of feldspar and other minerals, may be 
more distinct in alternating folia than they were originally. 
* H. C. Sorby, Quart. Geol. Journal, vol. xix., p. 401. 
Fig. G28, 
Lamination of clay-stone. 
Seguinat, near Gavarnie, in the Pyrenees. 
