THE 



GEOLOGICAL MAGAZINE 



NEW SERIES. DECADE VI. VOL. I. 



No. II.— FEBRUARY, 1914. 



I. — On * Cleat ' in Coal-seams. 



By Percy F. Kendall, M.Sc, F.G.S., 

 Professor of Geology in the University of Leeds. 



(PLATE III.) 



MY interest in cleat was first aroused by the study of the Geological 

 Survey memoir on the coals of South Wales (1908), from which 

 it became clear to me that the subject of the origin of anthracite was 

 intimately bound up with that of cleat. The object of the present 

 communication is, however, not directly connected with the anthracite 

 question, upon which I hope to have something to say when researches 

 upon which I am engaged with Mr. E. J. Edwards, M.Sc, of Cardiff, 

 have reached a more advanced stage. 



The ' cleat ', or system of joints traversing coal-seams, has strangely 

 escaped investigation by any British geologist during the past 

 half-century. But for brief and often conflicting references to the 

 phenomenon in textbooks, among which those in Professor J. Geikie's 

 Structural and Field Geology and Dr. Walcot Gibson's Geology of Coal 

 Mining must be signalized as the most valuable, and for more or less 

 casual allusions to it in papers by mining engineers, it might well be 

 imagined that all recollection of the existence of such a structure 

 had died out. The word 'cleat', or any alias by which it might be 

 indicated, finds no place in the Index to the first fifty volumes of the 

 Q.J.G.S., nor does it appear in the "Geological Literature added to 

 the Society's Library ". A search through about thirty memoirs 

 of the Geological Survey relating to coal-fields failed to yield a word 

 upon the subject.' Yet two quotations from earlier sources will 

 suffice to show that problems of surpassing interest are presented by 

 the disposition of the cleat in some British coal-fields. Jukes in his 

 Manual of Geology (1862), p. 212, says : " The large smooth vertical 

 surfaces [in a block of coal] are known by the name of ' the face ', 

 'the slyne', or 'the cleat' of the coal in different districts, the more 

 interrupted set being sometimes spoken of as 'the end' of the coal. 

 The ' face of the coal ' is the most necessary thing to attend to in 

 laying out the working galleries or gate-roads of a coal-mine, since 

 it retains its parallelism over very large areas." In a footnote he 

 adds: " /« inquiriiig of a collier in the Nottinghamshire coalfield in 

 the year 1838 as to the direction of ' the slyne ' (as the face is there 

 called), I was informed that it faced ' two o'' clock sun, like as it does all 

 over the icorld, as ever Iheered on\ hy which I understood that the sun 



^ Since this was written I heave learned that in the South Wales Coal-field 

 cleat is known as ' slips ' : with this clue I found an allusion to ' slip-cleavage ' 

 in the memoir above mentioned. It stated that there was none in anthracite. 



DECADE YI. — VOL. I. — NO. II. 4 



