72 SECTIONAL ADDRESSES. 



With great care it was possible to replace the slab in its original position 

 and to determine the orientation of the cleat to be N.W.-S.E. This 

 is not nearly the extreme of tenuity reached by well-cleated plant 

 remains. I have specimens that are mere shiny films, and cannot, I 

 should judge, exceed j^oth of an inch, yet they show well-defined and 

 regular cleat. Further, it should be noted that the production of cleat 

 was subsequent to the erosion of stream channels as well as to the pro- 

 duction of phenomena on the margins of the wash-outs. Every 

 pebble and flake of coal found in the displaced masses in these stream- 

 casts has the cleat well developed, and in strict parallelism with the 

 cleat of the adjacent undistui'bed seam. Whether its production was 

 later than the faulting has not been determined, and perhaps is in- 

 determinable, as the faults have not been shown to rotate the strata; 

 but, in the argument which follows, gix>unds will appear for regarding 

 the cleat as produced before the induration of the strata, and thei 

 faulting has evidently happened in the main after consolidation. 



In a paper which I contributed to the Geological Magazine in 1914, 

 I directed attention to the fact that cleat is quite independent of the 

 joints traversing. the shales and sandstones of the associated measures; 

 whence I drew the inference that the cleat must have been produced 

 prior to the jointing, for had the two sets of divisional planes been 

 produced simultaneously the agency that gave direction to the one would 

 have influenced the other, while if the jointing had been produced first 

 the coal could not possibly have escaped fracture by the joints. On 

 the other hand, if the intimate and regular cleating preceded the pro- 

 duction of the joints, no fresh fracturing would be requisite, or possible. 

 But the jointing of the measui'es may, or rather, must, be regarded 

 as an incident of the consolidation, so that, as a necessary corollary, we 

 must regard the cleating of the coal as preceding the consolidation of 

 the sediments in which the seams lay. This presents no a priori 

 difficulty, and it is corroborated by experience of lignite in unconsoli- 

 dated strata; for example, a bed of bright lustrous lignite lies inter- 

 bedded in the wholly soft and incoherent Eocene sands and clays of 

 Alum Bay in the Isle of Wight. This lignite, I find from a specimen 

 collected before my interest was aroused, is divided by a definite cleat, 

 but I did not make any observation of its direction. 



The reason for this early development of a joint system is easily 

 found — the original peat, in passing into lignite, acquired a brittle con- 

 sistency and a consequent disposition to joint. Indeed, the change of 

 consistency is the effect of chemical change and loss, whereby the peat 

 substance contracts. Hence, when our Coal Measures were first laid 

 down they would consist of a series of incoherent sands and muds, and 

 this uncompacted condition may have persisted for a very long period 

 so long as pressures were not excessive and no cementation took place ; 

 even surviving considerable tectonic disturbances, if we may judge by 

 the conditions of the Bovey Tracey beds. The peats, however, would 

 be subject to changes entirely innate : the gradual loss of volatile con- 

 stituents, or at least the resolution of the carbon compounds into new 

 groupings and the conversion of the mother substance of the coal into 

 lignite. In this condition the coal-substance would be brittle and liable 



