STRUCTURAL GEOLOGY 



395 



distinct. This sequence of events is sometimes shown by the trunca- 

 tion of laminae, and by other signs of erosion. The commoner sorts of 

 bedded rock are limestones, shales, sandstones, and conglomerates. 

 The bedding of limestones is often caused by films of clayey 

 material between the layers of limestone, the films causing natural 



Fig. 303. Cross-bedded sandstone. Maol Donn, Arran. The diagonal bed- 

 ding is conspicuous in the lower right-hand part of the figure. (H. M. 

 Geol. Surv.) 



partings. Sometimes, however, bedding arises from variations 

 in the physical condition of the calcareous sediment itself. Lami- 

 nation is not usually conspicuous in pure limestone, though it may 

 be well developed in. the shaly phases of this rock. Shales are nor- 

 mally laminated as well as bedded, and the lamination is often more 

 notable than the thicker bedding. Bedding in shale may arise 

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



