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. 



