7 2 DETAILS OF STRATIFICATION. 



subdivides to admit layers of sandstone, shale, and coal, which 

 gradually increase under Crossfell, and swell out to a vast thickness 

 in Northumberland, so as to contain several valuable seams of coal, 

 thick masses of sandstone, and abundance of shale, between the 

 horizontally separated beds of limestone. 



The Oolitic strata, near Bath, are composed of two portions 

 the Upper or Great Oolite, and the Inferior Oolite and between 

 them is a series of calcareous and argillaceous beds called Fuller's 

 Earth, sometimes one hundred and fifty feet thick. As we proceed 

 northward into Lincolnshire, the Fuller's Earth beds die away, thin 

 out, or are excluded from the series ; still farther north the whole 

 series is changed; so that in Yorkshire it includes thick layers of 

 sandstone, shale, and coal. On a first view the districts of Bath and 

 Yorkshire are very unlike, but the contemporanity of their deposition 

 is certain from the continuation of the same Oolitic beds and organic 

 remains through both of them. 



Thickness. The thickness of the beds or strata varies exceedingly, 

 and seems to have reference to the rapidity, regularity, and continuity 

 of the deposition, and the rate of consolidation of the materials. 



The Chalk is commonly about five hundred feet thick, and in all 

 this great mass we can scarcely trace any decided beds ; though the 

 layers of flint at equal distances, and the difference of the organic 

 remains at different depths, evidently prove a succession of stratified 

 deposits. 



The Great Oolite near Bath is, on the contrary, divided into a 

 certain number of beds, definite in quality, thickness, and order of 

 position. 



Laminae. A stratified rock, therefore, is composed of one or 

 more layers of strata, but this is^by no means the last term of the 

 analysis. Each bed is often composed of many laminae, which are 



Sandstone. 

 Laminated Beds. 



Limestone. 



Laminated Beds. 



Sandstone. 



Fig. 26- 



sometimes parallel to the plane of the bed itself, and sometimes lie 

 in it at different angles. Thus micaceous laminated sandstones, and 

 in particular the best flagstones of the coal districts, are composed of 

 a multitude of thin layers parallel to the plane of the bed, and en- 

 tirely covered by plates of mica, which probably cause the splitting 

 of the stone. This appearance is very analogous to the laminated 

 sand quietly left by the successive floods of a river. 



