50 Prof. Percy F. Kendall — On ' Cleat ' in Coal-seams. 



would shme directly upon it at two o'clock in the afternoon in an open 

 worh or that the planes rati about W.N.W. and E.S.E., and tvere 

 persistent in their direction in all my informanV s district at all eve?its." 

 He quotes John Phillips's Report on Cleavage and Foliation in Rocks, 

 etc, in the 13. A. Report for 1856, and I give the passage in extenso : — 



"§ 11. 17ie Cleat in Coal. 



" In the northern coal districts of England, and in other tracts, 

 there exists, besides the lamination parallel to the bounding siirfaces 

 of the beds, a series of approximate, often nearly vertical divisional 

 surfaces, aloug which the coal admits of easy fissility. This structure 

 is called cleat, and it is of the greatest importance in coal working, 

 since parallel to it the headways are driven in the ' post and stall ' 

 workings of Jforthumberland and Durham, and parallel to it the 

 ' banks ' are wrought in the ' long wall ' and ' bord and end ' systems 

 of Yorkshire and Derbyshire. Cleat is little afPected by fractures or 

 undulations of the strata. It has usually one persistent course across 

 a large district, — the same direction often obtains in neighbouring 

 districts, and even prevails over the whole of a great Carboniferous 

 region. Thus in Northumberland and Durham the cleat runs most 

 generally to the north-west (true) ; its ' strike ' is in that direction. 

 The most general strike of the beds is to N.N.E. The same direction 

 of cleat is prevalent in Yorkshire and Derbyshire, and this whether 

 the beds strike eastward, as near Leeds and Sheffield, or southward, 

 as near Huddersfield and Chesterfield. The same direction prevails 

 in Lancashire." 



In reading this pregnant passage one scarcely knows which feeling 

 is uppermost — admiration for the marvellous industry and insight 

 of Phillips, or astonishment that his generalization attracted so little 

 of the attention of either his contemporaries or successors. So far as 

 the Yorkshire Coal-field is concerned, his statement of fact is endorsed 

 by all mining engineers with whom I have spoken, and I shall add 

 some corroboration of my own. 



The particular aspect of the subject to which I wish now to 

 apply myself is the absolute independence of the cleat in coal-seams, 

 not only to the lie of the rocks, but also to the jointing of the 

 measures in immediate association with them. This relation is not 

 explicitly indicated by Phillips, though it is perhaps implied by his 

 statement that the direction of cleat maintains its constancy despite 

 diametric changes of dip. 



I will first substantiate the constancy of cleat by a few examples 

 taken at random. All the bearings are magtietic. 



Southowram, near Halifax, cleat . . . N. 17° W. 



joints in roof N. 63° W. 

 N. 39°E. 

 Robin Hood Quarry, near Wakefield, cleat . . N. 43° W. 

 Wheldale and Fryston, cleat . . . . N. 22° W. 



Allerton Bywater, cleat N. 25° W. 



Whitwood, cleat N. 28° W. 



The total variation of direction in these readings is 26°, or taking 

 N. 30° W. as the direction most commonly observed in this coal-field 

 the deviation is 13° to the west and 13° to the east. 



