Ch. XII.] NATURE OF STRATIFICATION. 249 



the surfaces of cleavage in the fissile granular slate marked 

 with superabundant mica, and from observing that the 

 organic remains were laid in the same parallels, it appeared 

 that the laminae of cleavage are indeed those of deposition. 

 But these conclusions will hardly apply to the unmicaceous 

 slate rocks ; for, though near Horton, the large tables of slate 

 have knots parallel to their surfaces, and are even separated 

 by softer greenish layers, yet the level top of this series, as it 

 lies exposed for miles under the limestone scar, must still 

 make it hazardous to decide that the planes of cleavage and 

 stratification are here coincident. And it is so often found 

 in the slate of the middle division in the Lake district, that 

 the planes of cleavage cross alternate layers of finer and 

 coarser matter, that they may be considered as at right angles 

 to the strata." " Next to the cleavage planes, the most con- 

 stant of all the great joints are those which cross the cleavage 

 nearly at right angles, in a vertical direction." 



Now, compare this with what has been stated concerning 

 the structure of the Cornish slates, in the sixth chapter, and 

 it will be seen that these rocks are similarly constructed. 



The beds of the greywacke and carboniferous series exhibit 

 the same kind of structure ; but the higher we ascend in the 

 series, the greater is the difficulty, in many cases, in distin- 

 guishing the parallel layers from the effects of deposition. It 

 has, however, also been noticed in the oolitic group, and is 

 well known to characterise the gypsum formations. "At 

 Hedington quarries, near Oxford, and at Anthony Hill, near 

 Bath, the laminae of the freestone are inconformable to the 

 larger divisions. And, at Buckland Point, in the parish of 

 Mells, Mr. Townsend found rhomboidal beds of oolite trun- 

 cated, perfectly smooth in the superior and inferior surfaces, 

 dipping at an angle of 40, and confined between two hori- 

 zontal beds of clay." * 



But why multiply examples ? A sufficient number of facts 



* Greenough's Geological Essays, p. 18. 



