232 
POPULAH SCIENCE ItEVIEW. 
liar appearance, from the immense number of the nodules and 
the regularity of their arrangement. 
The more ancient limestones, formerly called primitive, 
which are usually more or less crystalline in texture, are fre- 
quently found to be foliated with chlorite or mica (as at In- 
verary), with augite and scapolite (as in the Hebrides), or with 
spinel and chondrodite (as at Christiansand, in Norway) ; other 
minerals might also be mentioned as inducing such structure 
in the metamorphic limestones. In some instances the folia- 
tion of different parts of the same large mass of crystalline 
limestone may be brought about by minerals very different in 
character to one another, as shown in the annexed figure. 
Fig. 2. 
This woodcut represents a section of a limestone quarry, near 
Christiansand, in Norway, in which a denotes the overlying 
granite ; a, 6, c, different varieties of crystalline schists in 
irregular patches ; d , coarsely crystalline white limestone or 
marble ; e, crystalline white limestone, foliated by small crystals 
of augite and scapolite ; /, ditto, foliated by mica. Although 
in this section we find a somewhat confused arrangement of 
the different rocks, it is seen that the general direction of 
the lines of foliation remains constant, quite independent of 
the different character of the minerals by which they are ex- 
pressed, or the nature of the rock which they traverse. 
It must not be supposed, however, that the foliated structure 
in rocks is only developed by mineral silicates, as in the in- 
stances hitherto referred to ; on the contrary, other and most 
distinct compounds frequently make their appearance : thus 
