PTERICHTHYAN PERIOD. 173 



very simple proof of this is to be seen in the valley of the Lune 

 at Kirkby Lonsdale. Here the valley, excavated in the Upper 

 Silurian strata, is filled to a considerable extent with conglome- 

 rates of Old Red, full of pebbles of the lower groups of Hougill, 

 and the other high slaty fells which give springs to the Lune. 

 In other situations the Old Red rests on older beds of the slaty 

 series, so as to be clearly unconformed to the whole of it. From 

 this it follows that those older strata had been greatly disturbed, 

 placed in new positions, and excavated into valleys, and that 

 these valleys were filled with the violently aggregated detritus, 

 which had been swept down them from about their sources. 

 It is probable they formed land, and gave birth to streams, which 

 ran down valleys into estuaries, and entered seas now obliterated 

 by later convulsions. 



In Yorkshire we have no trace of these very ancient valleys, 

 no conglomerates of the Old Red ; but we see, in the region below 

 Whernside, Ingleborough, and Penyghent, the displacement of 

 the old slaty strata ; the dips in various directions which they 

 have acquired ; and, what is very remarkable, the summits of the 

 anticlinals thus occasioned are ground, worn, or rather, we may 

 almost say, planed down to a nearly level surface (some bands 

 are a little prominent as being less abraded), and this surface is 

 covered and preserved to us by nearly level strata of mountain 

 limestone, contrasting strongly with the highly inclined slate, 

 and containing in their lowest beds pebbles of that slate. (See 

 PI. 31.) 



This is the fact, and most remarkable it is. What is the ex- 

 planation ? According to modern geology this is the effect of 

 the sea, acting, as we see it act in particular cases, on a shore* ; 

 it is the gradual work of the breakers of a Palaeozoic sea; an 

 effect anterior to the deposition of the mountain limestone, and 

 probably part of that system of natural agencies which roughly 

 excavated the valley of the Lune, and filled it with conglome- 



* See De la Beche's Geological Observer for excellent observations on 

 this subject. 



