270 MATERIALS AND THEIR ARRANGEMENT 



the films causing natural partings. Bedding arises also from varia- 

 tions in the physical condition of the calcareous sediment itself. 

 Lamination is not, as a rule, conspicuous in pure limestone, though 

 it may be in the shaly phases of this rock. Shales are normally 

 laminated as well as bedded, and the lamination may be more 

 notable than the thicker bedding. Bedding in shale may arise 

 from the introduction of sandy laminae, or by changes in the texture 



Fig. 244. Cross-bedded sandstone. Maol Donn, Arran. The layers are 

 horizontal, some of the laminae, diagonal. (H. M. Geol. Surv.) 



of the mud, etc., of which the shale was made. Some sandstones 

 are divided into beds by shaly or clayey partings, or by variations 

 in the coarseness or coherence of the sand itself. Sandstones may 

 be thick or thin-bedded, and their bedding passes insensibly into 

 lamination. 



Sand is deposited normally in relatively shallow water where 

 it is subject to much shifting before it finds permanent lodgment. 



