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erperience now. In post glacial times our country was roamed over by the 

 mammoth, the long-haired rhinoceros, the bison, the cave lion, and the cave 

 bear. The mvtsk ox, and the marmot, were also inhabitants of the country, and 

 the presence of arctic plants in the post-glacial clays of Devonshire tell us of the 

 bitter cold that still lingered in the vales of southern England, where now grows 

 the myrtle and the vine. And he who wanders among the hills of Wales and 

 would decipher the history of its boulder drifts, its disintegrated rocks, it» 

 vales, and rounded hills, or bluff escarpments, must bear in mind that he has 

 post-glacial action to register, the action of snows, glaciers, and frosts which 

 were prolonged into comparatively late times, as well as the action of present 

 subaerial agents and the action of existing rivers, springs, and brooks. It is 

 geological nonsense to talk of the valley of the Usk having been eroded by the 

 existing Usk or an Usk like the present. The Usk was a very different stream 

 to the present when swollen by melting snows, or large ice masses and boulder 

 rocks rushed down its stream, and this happened in post-glacial times, as any 

 observer may see for himself if he will trace the old river drifts from Abergavenny 

 to its source. No one is more convinced of the endless, steady results of modem 

 denudation, if I may so express it, more than myself, but there are scored upon 

 the hills and vales of "Wales the witnesses of other denuding powers than are now 

 present there, the no longer existent powers of ice and melting snow, of torrential 

 rivers and of bursting lakes. Rains, springs, and frosts are engaged widening 

 and deepening our valleys now, but there was the action of land ice and 

 glaciers, and at sea icebergs at work modifying the land we now live in, 

 in Postglacial times, and that kind of denudation has now ceased in Wales. 

 I do not therefore think it philosophical to attribute the contour of scenery wo 

 now behold to causes now in existence in this country, when some of the 

 principal agents have passed away. Rain and rivers have done much, no doubt, 

 in moulding the scenery of this beautiful district — and of every other district — 

 but they have not done all ; and he who would attribute everything to rain and 

 liver agency only rides his hobby to death, and brings ridicule upon philosophy. 

 The Carboniferous limestone of the South Welsh coal field forms a girdle 

 ti that great coal field, and ever j' where dips vinderneath the carboniferous grit 

 and coal measures. But I should like to be able to show you two outliers 

 which are cut off from the rim of the coal field between Merthjrr and Brecont 

 and which are surrounded by Old Red Sandstone which has been denuded of the 

 Limestone, the JliUstone grit, and all the Coal measures. They lie to the east 

 of the road between Blerthyr and Brecon, and among the beautiful glen scenery 

 of Abercriban and Cwm Cellan. The most remarkable of all the mountain 

 Umestone outliers in the neighbourhood of the South Wales coal field is Pen 

 Cerrig Caleb (the Top of the limestone crag), wMch was selected, through its 

 name, by Sir Roderick Murchison, when engaged upon that noble work, the 

 "Silurian System." He ascended the Black Mountains in order that he might 

 ascertain why such a name had been used in a district appearing to consist 

 exclusively of Old Red Sandstone. This insulated outlier of Mountain lime- 



