464 J. G. GoodcJiild — Weathering of Limestones. 



planes of easy solution were evidently in process of development. 

 Some of these were following the original planes of deposition of 

 the rock ; others tended to work in along the' bate, or those obscure 

 planes of separation along which direction, as masons know, the 

 rock will dress more readily than along others. Other planes again, 

 artificially induced, were being etched parallel to the dressed surface, 

 as Prof. Judd had shown to be the case with the worked flints 

 employed for outdoor masonry. Altogether, a careful study of the 

 phenomena of erosion presented by these dated tombstones, pointed 

 to the conclusion that the rate of waste now in progress will, in a 

 few years, be very greatly accelerated by the multiplication of the 

 surfaces presented to the denuding agents. We might, therefore, 

 safely assign to this rock a rate of destruction treble or quadruple 

 that given in the estimate above. Weathering soon reveals the 

 existence of the ' bate ' in limestones, and detaches flake after flake, 

 parallel to the joint planes, with comparative rapidity ; almost as 

 if the bate or grain of the rock represented some kind of cleavage 

 affecting the whole mass of the limestone. On the vertical face of 

 limestone scars, or in the same position in limestone waterfalls, it 

 is very evident that the chief waste of the rock is effected by this 

 constant flaking off of thin slices of weathered rock detached by 

 weathering along the bate of the rock. The flakes fall, expose an 

 inner face to the action of the weather, and are themselves soon 

 dissolved and carried out of sight. 



There is, of course, very considerable difference in the rate at 

 which different limestones tend to waste before atmospheric agencies. 

 Those which contain an unusual percentage of argillaceous matter 

 appear to waste at the highest rate ; and this is the more especially 

 the case if the rock in question has been more or less dolomitizecl, 

 as have many of the Carboniferous Limestones that have formerly 

 received magnesian infiltrations from the New Bed Eocks — the 

 commonest source of dolomitization in Britain. At the other 

 extreme (so far as the writer's own observations go) stand the 

 compact, well-bedded, limestones that include much bituminous 

 matter in their composition. But the rate of waste of bituminous 

 limestones is by no means a low one under favourable circumstances, 

 as the following observations will show : — About forty years ago 

 a very hard, compact, bituminous limestone, belonging to the 

 Yoredale Series, had been broken up for road metal, on a cart road 

 leading to a fell-side coal mine near Tailbrig, Westmoreland. After 

 a time, the coal mine, and consequently the road leading to it, ceased 

 to be used. So the road was left for about twenty-five years. The 

 nature of the surface in the higher part of the road favoured the 

 passage over it of thin sheets of surface-water, charged more or less 

 with compounds derived from the decomposing vegetable matter 

 of the moorlands above. After the interval mentioned above had 

 elapsed, the present writer happened to notice that the limestone 

 " macadam " had evidently undergone many changes in consequence 

 of its prolonged exposure. The surface of the whilom angular 

 fragments of limestone was etched and corroded into irregular pits 



