160 E. C. Martin — Source of Lbnedone Pebbles 



upheaval aud denudation of coal-beds were going on pari passu with 

 the deposition of the workable coals, a condition of things required, 

 as it seems to me, to account for this coal pebble. 



Perhaps the most interesting and instructive point in the story of 

 this coal pebble lies in the fact that whilst the central seams of coal of 

 the Middle Coal-measures were being laid down in a quietly subsiding 

 bay or flat, underlying or older beds of completely formed coal, etc., 

 not so very far away, were, by the waves, being reduced to mud, sand, 

 and gravel, on flats composed, of which grew trees, etc., at about sea- 

 level. 



Lithology. 



Now, this is not a water-worn or rounded piece of wood, or frag)%€nt of 

 a tree, but a lond-fide pelhle of that puzzling compound we know as 

 coal m coal. It furnishes still another instance of what has always to 

 the author been a conundrum, a seeming paradox in lithology, which 

 is this : How is it that pebbles or fragments of rocks in the shape of 

 inclusions or individual bits composing a conglomeratic or brecciated 

 mass enclosed in a stratum of normal rock, are, to all appearances, not 

 dissimilar from the enclosing bed in its normal or undisturbed condition ? 

 e.g., you get pebbles and fragments of Carboniferous Limestone in the 

 shape of a conglomerate in what to all outward appearances seems to 

 be a normal stratum — iron-ore fragments in iron-ore beds ; bits of 

 slate in a slaty massif ; rounded sandstone in sandstone beds, and so 

 on — in short, rocks calcareous, arenaceous, siliceous, argillaceous, 

 carbonaceous, etc. The question that puzzles me is, ivhy is not noio 

 tlie coal pelhle of ordinary coal, in a seam of the ^^^rae, farther adcanced 

 towards a condition of anthracite, since it must have been exposed for 

 vast ages to further mineralizing influences since burial — its second 

 burial — in the seam? And it is just as hard to explain why or how 

 the substance of such a pebble had arrived at maturity as to its 

 condition as coal during the Middle Coal-measure period, for the very 

 aspect and nature of the pebble speaks for itself ; it was just as much 

 coal then as it is to-day, apparently neither more nor less so ! That is 

 just where the inexplicable seems to come in ! ' Inclusions ' seem to 

 have been incapable of receiving further metamorphism on becoming 

 inclusions. The facts seem to point to solidiflcation of sediments, 

 coupled with hardening, shrinkage, jointing, and other rock-forming 

 processes as having operated to the completion of the normal stage — 

 the strata as we now have them — very rapidly indeed after burial. Is 

 not this a phase of our science not yet much understood, and certainly 

 a difficult but most interesting problem for observers to help solve ? 



Y. — The Phobable Source of the Limestone Pebbles in the 

 BuNTEE Conglomerate or West Somerset. 



By Edgar C. Martin, B.Sc, A.I.C. 

 (WITH A MAP.) 



WHEjS" the Budleigh Salterton Pebble-bed is traced northward 

 into Somerset it loses its unconsolidated character and passes 

 into a calcareous conglomerate. The change takes place north of 

 Burlescombe, and is complete at Thorne St. Margaret ; thence to 



