16 Mr. Phillips on a Group of Slaic Rocks 



This occurrence of pebbles in the lower beds of the mountain limestone is 

 not confined to the district in question. I have collected such specimens at 

 Underbarrow Scar near Kendal, and at Winder Moor near Ulswater, in 

 neither of which places is any old red conglomerate known to separate the 

 limestone and slate, though it occurs in lower ground in the neighbourhood 

 of both localities. 



On the Siralijicaiion of Slate. 



Few subjects are involved in greater difficulty than the question of the stra- 

 tification of slate. We see this rock divisible into layers, and sometimes ob- 

 serve these layers alternately of finer and coarser texture, — appearances which 

 in shale would be deemed very satisfactory evidence of the laminas of deposi- 

 tion ; but the generally vertical direction of the layers or planes of cleavage, 

 and the numerous geometrically intersecting joints, leave much doubt in the 

 case of slate. 



This difficulty is not lessened by the fact, that, in many kinds of slate, there 

 are really two cleavages or sets of laminee, made evident by particular circum- 

 stances of weathering, though generally only one which may be called the true 

 cleavage* is practicable by blows. The oblique laminae of false cleavage form 

 what is technically called the "bate" of the slate; and, though less evident 

 than those of the true cleavage, are generally regular and parallel to each 

 other, and intersect the planes of true cleavage at certain angles constant for 

 the same quarry ; as in the thick slate dug near Horton in Ribblesdale. But 

 sometimes these oblique laminae change their direction in passing through 

 contiguous layers of true cleavage, as in Leek Beck near Kirby Lonsdale. It 

 is in consequence of the oblique intersection of the laminae of bate and clea- 

 vage that the slates dug at Horton so generally break with edges bevelled on 

 one side as to be called " Sheerbate stone.'' 



From finding the surfaces of cleavage in the fissile granular varieties marked 

 with superabundant mica, and from observing that the organic remains were 

 laid in the same parallels, 1 have been induced to conclude that in these va- 

 rieties of slate (as in sandstone, to which their composition seems analogous,) 

 the laminae of cleavage are indeed those of deposition. 



But this conclusion will hardly apply to the unmicaceous slate rocks ; for 

 though near Horton the large tables of slate have knots parallel to their sur- 

 faces, 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 



* Called "Spires" by the workman. 



