11 



always fossiliferoua. It is worthy of consideration whether the deep sea con- 

 ditions which I have suggested as the origin of the former, and the bttoral 

 conditions which seem more prohably to have given origia to the latter, help to 

 account for this difference. 



I had intended entering into the palceontology of our Cornstones, but 

 think it is better to defer this to another occasion, when it may be jwasible to 

 discuss the subject more fully. For the present I Iiave treated them merely as 

 deposits of lime, and in connection with this I may refer to the Springs of the 

 Old Red Sandstone being so often hard or calcareous. AVater contaiuiug carbonic 

 acid has the power of dissolving one thousandth part of caiboiiate of lime. Rain 

 water contains this gas, and becomes further chargeil with it by passing through 

 decomposing vegetable matter. Then, as it percolates thiough the marls and 

 Cornstones, it becomes loaded with lime and issues forth again as a calcareous 

 spring. Some of the springs in this neighbourhood are highly charged with lime. 

 We shall pass in our walk to-day, at least three springs, in which the lime is bo 

 abundant that it is copiously deposited on any object placed in them, thus 

 constituting what we commonly know as petrifying springs. From such springs 

 amongst our hills the lime is often deposited as Travertine, as tlie water trickles 

 over the rocks. On the contrary, tlie abundant spring which supplies the town 

 of Abergavenny arises in the upper part of the Sugar Loaf above tlie Cornstone, 

 where there is, perhaps, 500 feet or more of standstones, without either corn- 

 stones or marl, and the water is remaikably free from lime ; whilst on tlie other 

 hand, in the spring of the lower range of the Little Skirrid, whicli contains 

 both marls and cornstones, the water is abundantly charged with lime, and is 

 therefore very hard. 



The Cornstones have played no unimportant part in giving the country its 

 present outlines of hills and valleys. Many of the bands are exceedingly hard 

 and tenacious, and much better fitted to resist denuding agencies than the 

 mai'ls and most of the sandstones. That they helped to withstand the powers 

 which scooped out our valleys in the past there can be little doubt, and that 

 they resist the disintegrating influences of the present we may see in the 

 escarpments of the Black Slountains where, although the adjoining sandstones 

 have crumble<l away, bands of Cornstone may be seen standing out sharp and 

 unaltered, and only tumbling down ultimately in large masses when they have 

 become undermined by the disintegration of the underlying strata. Their 

 greater durability is also shewn by the fact that although they form but a small 

 portion of a mountain the large masses of rock lying at its base are often 

 chiefly cornstones, most of the sandstones havit^ disapjieared. The same resist- 

 ing agency may be seen sometimes in the valleys where a river which has cut 

 down through the softer strata is long arrested by a band of cornstone. 



