File:The Quarterly journal of the Geological Society of London (12711575993).jpg

1855..
FORBES FOLIATION OF ROCKS,
107
(Case 2.) — At Jsegersborg, near Christiansand, in Norway, the
foliation of a highly crystalline white limestone in schist was found
to be parallel with the apparent lines of bedding (see fig. 1). It
Fig. 1. — Section of foliated limestone and gneiss at JiBgersborgy
near Christiansand. (See also page 173.)
Height of Section about 8 feet.
A. Granite.
a, a. Ordinary gneiss.
b, Quartzose gneiss.
c, c. Gneiss.
df d. Crystalline white limestone,
e, e. Augitic limestone.
f,f. Micaceous limestone.
will frequently, however, be found very difficult to prove satisfactorily
when the line of foliation coincides with that of bedding ; as in many
cases, and particularly in Norway, there are rarely any normal stra-
tified beds in so close contact as to render the matter perfectly
indisputable.
Keilhau seems, however, to consider the cases where the foliation
does not agree with the stratification as exceptional, and mentions*,
evidently with this impression, a case where he has observed in
Thelemarken a thick bed of very characteristic gneiss situated
amongst other crystalline strata in which the mica and gneiss struc-
ture, as a whole, was developed at right angles to the real planes
of stratification.
It is possible also that the coincidence of foliation and stratifica-
tion would be found much more frequently the case, were it not for
the very general occurrence of the disturbing influence of a pre-
viously existing cleavage-structure, — or of a more or less inclined
position of the beds during the time foliation occurred, — or, lastly,
of the intrusion or approach of igneous rocks.

• Norske Mag. for Naturvidenskab, New Series, vol. i. p. 70.