BY SlJGH MILLER. 331 



aside, that in Cretaceous times ''only a few insignificant islets 

 rose above a waste of chalk-depositing waters," where Britain 

 is now. One thing is certain ; this region answered — if I may 

 so express myself — to one of the smooth spaces of the cut-glass. 

 Nothing can be founded on the mere absence of deposits. 



It is important to observe, however, that the Tertiary lavas 

 of "Western Scotland and the iN'orth of Ireland were spread out 

 upon a land-surface, on which waste was at work all through 

 the fiery ei-a.* Eocene and Miocene ages were passed in a vain 

 strife of the two elements, water and air, against the other two ; 

 but in the Pliocene the scale turned, and the volcanic products 

 have now suffered great denudation. By it the greater portion 

 of these piles and sheets of lava and ashes have now been re- 

 moved ; and outlying caps of lava, separated by miles of ancient 

 gneiss that bear no trace of its former covering, or by miles and 

 leagues of sea, are some of its witnesses. I will describe the 

 instance I personally know best. Voyaging up that western Scot- 

 tish coast an island is seen with what might be taken for a huge 

 peel-tower on its summit. The island is one of a group of insular 

 outliers of Miocene lava, and is about eight hundred feet high ; the 

 toiver adds well nigh five hundred feet to its height, and is a mass 

 of newer pitchstonc. It sounds like romancing that the pitchstone 

 now crowning an island was once run into the mould of a valley 

 perhaps as deep as Tynedale, in that Miocene basalt ; but denu- 

 dation, largely of an atmospheric kind, has assuredly worked this 

 change between an old land surface and a tower-like h eight. f 

 Other instances might be multiplied. The old volcanoes, that 

 '•rivalled Etna in height," are now wasted down to stumps, — 

 and mountain-forms have been sculptured out of ' ' intensely hard 

 cores" of rock, by the same subaerial action that has in Tynedale 

 produced escarpments on the watersheds ; and it is probable that 

 in this atmospheric denudation Northumberland shared. The 

 scalpel of denudation, in laying open the anatomy of the country, 



* Ah elucidated by the Duke of Art^yll, I'rof. Geikie, and I'lof. JmUl. 



t Professor Geikie was the first, amons many oliservcrs, to solve this curious puzzle of 

 a river course "set on an hill In the Island of I-igg'." Quart. Jour. Gcol. Soc., Vol. 

 XXVII. 



2 .V 



