FALSE BEDDING. 



73 





False Bedding. But the coarser flagstones of the same coal dis- 

 tricts are often composed of laminae, laid at various angles to the plane 

 of the bed, and in consequence producing a rough, uneven, shattery 

 surface, and a tendency to oblique fractures. 



Such appearances of oblique lamination are occasionally found in 

 the modern sediment of agitated waters, both in the banks of rivers, 

 in estuaries, and on the sea-shore. 



When these oblique laminae extend through thick beds, they some- 

 times cause a slight difficulty in determining the dip of the strata, and 

 are then called false bedding. Some of the coarse upper beds of the 

 Great Oolite of Bath, Gloucestershire, Northamptonshire, and Lincoln- 

 shire, as well as of Normandy, are remarkable for this false bedding. 

 But it is in the coarse sandstones that we see the most remarkable 

 examples of this structure, as in the Oolitic sandstones, &c., on the 

 coast at Scarborough, and in the Trias rocks under Nottingham Castle, 

 and it is generally seen in valley gravels. False bedding, oblique 

 lamination, or current bedding, is indeed one of the most characteristic 

 features of shallow-water deposits, and is never observed in clays. It 

 is due to changes in the directions of the currents which accumulated 

 the deposit, and we can often discover from the inclination of the 

 laminae the directions from which the current flowed which formed 

 each of the successive beds. 



In this diagram the layers i and 2 in the face of the section might 

 supposed to be regularly bedded 

 id upheaved, for colour accumu- 

 ites in the laminae and is often 

 cashed out of the planes of strati- 

 ication, but a glance at the other 

 dde of the section shows at once 

 it we have a case of current 

 Iding. Bed i is seen by the 

 )mpass points to have been formed 

 )y a current flowing from the east ; 

 then the current changed, and 

 owing from the north-east cut off the tops of the first set of laminae, 

 d threw down bed 2. In bed 3 the current comes from the north. 

 The more violent the action of the water, the less regular is the 

 ternal constitution of the layers found beneath it. Let any one with 

 his view compare the effects of the tide beating upon the sand and 

 bbles of the eastern coast, or the tumultuous products of a mountain 

 iver, with the tranquil deposit and sediment on the alluvial lands 

 ear Lynn and near Hull. In the former case the materials are fre- 

 uently found heaped together in laminae, variously and confusedly 

 inclined to one another ; in the latter they are all parallel to the 

 " orizon, and to the general plane of the surfaca The former case, 

 the shore lamination, is analogous to the false bedding mentioned in a 

 preceding section, so general in our sandstones and conglomerates, and 

 in shelly beds of Oolite ; the latter is exactly like the regular lamina- 

 ion of clays and shales. Like effects flow from like causes, and thus we 



Fig. 27- 



