io4 



HARDWICKE'S SCIENCE-GOSSIP. 



of the sea bed, so as to allow the accumulation in 

 direct succession of some 10,000 feet of strata. To 

 an ungeological ear this may sound astounding, but 

 further acquaintance with the phenomena of even this 

 small district will reveal matters which may appear 

 still more startling. 



Thus far I have only spoken of the character of the 

 Skiddaw slate as a formation, and of the physical 

 conditions under which that formation was deposited; 

 later on I shall have occasion to describe how these 

 marine deposits were uplifted, curved and contorted, 

 changed, cleared, and hardened, and how at last the 

 smooth slope of Skiddaw, the deeply ruined front of 



the district, I have called the Volcanic series of 

 Borrowdale. The rocks of this series must now be 

 described as to character, and their mode of formation 

 entered into. 



I have said that they are volcanic, most of my 

 readers will therefore at once form some idea of their 

 nature. Every one has seen the light pumice-stone 

 and specimens of lava brought from some modern 

 Volcanic mountain, and will remember that one 

 conspicuous characteristic of such rocks is the fact that 

 they are often more or less riddled with holes, or are 

 vesicular, as it is called. All know too, that lava is 

 emitted from volcanoes in a more or less fiery liquid 



MARYPORT 



F R A ME WO 



U.SILURIAN 

 VOLCANIC. 

 SKIDDAW SLATE. 



ALL GRANITIC 

 MASSES 

 OMITTED 



Fig. 61.— Sketch Map, showing the principal Geological Formations in the Lake District. The Lakes 



are the only physical Features indicated. 



Blencathra, and the craggy face of Grasmoor, were 

 carved and sculptured ; in the mean time let it be 

 remembered, that for us in the present stage of our 

 historic knowledge, some 10,000 feet of mud and sand 

 lie accumulated beneath a shallow sea at the close 

 of the so-called Skiddaw slate period. And what 

 followed ? 



Between the two south-west and north-east bound- 

 ary lines that I have already described, and which 

 are placed on the rough map (fig. 61) to help the eye, 

 lies another great thickness of rocks of a volcanic 

 character, which from their full development in 

 Borrowdale, that most beautiful of all the dales in 



state, and that in streams it flows down the sides of 

 the volcanic cone. It quickly cools at both under 

 and upper surfaces ; in the one case from coming in 

 contact with the cooler ground, and in the other from 

 its exposure to the air. Not so the interior, however. 

 This retains its red heat long after it is quite possible 

 to walk upon the cool crust. From the surfaces of 

 the lava the imprisoned gases readily escape, hence 

 the many vesicles ; but if the floor be of any thick- 

 ness, the interior, cooling more slowly, assumes a 

 solid and compact appearance with few vesicles. 

 Such is the general outward aspect of lava-rock as 

 you may see it on the flanks of Vesuvius, or on the 

 sea-shore at the foot of that volcano. Oftentimes 



