HARDWICKE'S SCIENCE-GOSSIP. 



105 



in cooling, also, the shrinkage produces jointing in 

 the compact rock which frequently assumes a columnar 

 form. The sea-worn ends of such columns you may 

 walk over on the shore beneath Vesuvius. Sometimes 

 instead of definite columns the rock is divided up 

 into rude spheres. 



Now we may return to our Lake District, and upon 

 many of the mountains included in the area of the 

 Volcanic series, may find rocks almost precisely 

 bimilar. Could the reader climb with me up the 

 Falcon Crag hillside, overlooking Derwentwater, we 

 might see beds of lava cropping out, as it is termed, 

 upon the hillside, very similar in appearance to 

 lavas of a modern volcano ; the same vesicular and 

 irregular upper and lower surfaces, the same compact 

 interior, and in one case (two-thirds of the way 

 up the steep side) a thick compact lava with a 

 curiously curved tubular and globular jointing.* The 

 same likeness to the modern lava occurs again and 

 again, though in many cases the vesicles formed 

 by the ancient escape of the volcanic gases are 

 filled with various mineral matters which have been 

 deposited from water holding them in solution 

 during the long ages since first these lavas flowed 

 from the old volcanoes. Subsequent weathering on 

 exposure to the atmosphere, has however frequently 

 emptied the cavities once more and restored the 

 ancient look. I might proceed further and show that 

 not only in the lavas of the lake country are there 

 representatives of several different classes of modern 

 lavas as to mineral and chemical composition, but 

 also that the internal microscopic structure and 

 arrangement of those minerals are very much the 

 same, and follow the same general laws in both cases. 

 For the evidence of this however, the reader must be 

 referred to the already published Memoirs and papers. 

 So that taking the evidence all round, there cannot 

 be a shadow of a doubt that we have among our 

 Cumbrian hills, true lava-flows emitted from some old 

 volcanic centre or centres. 



If stronger proof were needed, the deposits of 

 so-called volcanic ash supply that proof, for as 

 .around modern volcanoes there are scattered far and 

 wide, accumulations and beds of fragmentary matters 

 of all sizes thrown out from the vent, from the finest 

 produce to blocks as big as small cottages, so in the 

 Lake District do we find similar accumulations and 

 beds of like fragmentary material, now, however, 

 compacted together into a hard rock, in which, never- 

 theless, the fragments are generally discernible. In 

 some cases, indeed, subsequent alterations (heating 

 under pressure, &c.) of these old ash deposits may 

 partially, or even entirely, conceal the original 

 structure, though this may often be revealed on 

 weathered surfaces of the rock when the interior 

 .shows no trace of that structure. The ash ejected 



* The various beds seen in this hillside, less than a mile and 

 .a half from Keswick, are described in detail in my Memoirs on 

 the northern part of the English Lake District (H.M. Geolog. 

 Survey), pp. 13-16. 



from Vesuvius has often been showered down into 

 the waters of the Bay of Naples, where it has been 

 sifted and bedded so as doubtless to form regular 

 layers at the bottom of that sea. The finest ash, 

 such as that which enveloped Herculaneum and 

 Pompeii, often presents also a distinct and very 

 finely-bedded appearance, sometimes increased by 

 the fall taking place along with deluges of rain. In 

 our home district there is plenty of the same finely- 

 bedded ash, much of which may have been actually 

 deposited in water, while the rest may have fallen 

 much as the ash just alluded to fell, when the towns 

 of Herculaneum and Pompeii were overwhelmed 

 by it. 



Several traverses of the mountains formed of 

 these volcanic rocks will give abundant examples of 

 ash deposits of all degrees of fineness and coarseness, 

 and there are some cases where tall crag-faces are 

 seen to contain within them mighty fragments of 

 several yards in length. 



But some will say there is yet one thing wanted to 



make this proof complete, and that is, that the actual 



volcano, the actual centre, or vent, from which these 



deposits were emitted, be shown. There are two 



reasons, however, which make this peculiarly difficult 



in the present case : one is, that the age of these 



deposits is extreme, and the actual volcanic cone 



consequently very liable to be completely obliterated 



in the lapse of ages, and the other reason is, that a 



large portion of the volcanic area doubtless now lies 



buried beneath more recent deposits, and among 



these now hidden portions one or more of the old 



centres may be buried. There are, however, several 



bosses of igneous rock in the district, and I will 



especially call attention to one, namely, Castle Head, 



Keswick. This rock, in all likelihood, represents 



the plug, as it may be called, of an old volcano. 



Imagine the fires of Vesuvius to die out ; the liquid 



lava now rolling up and down in the funnel to cool 



slowly into an exceedingly hard and compact rock, 



differing in some respects from the lava which had 



flowed out in sheets, on account of the different 



conditions under which they respectively cooled. 



Then further imagine that, during a long course of 



ages, the atmospheric powers, the rain and running 



water, and the action of the sea along the base of 



the cone, as perhaps it was slowly depressed beneath 



the waves, all so far obliterate the old volcanic 



mountain as to destroy its form, perhaps leaving partly 



upstanding the hardened plug and some of the 



original beds in cliffs here and there. Imagine this, 



and you have an idea of a little of what has taken 



place with the old Cumberland volcano or volcanoes, 



so that Castle Head may yet represent an old volcanic 



centre, of which but the hardened plug of the old 



volcano remains, while the lava and ash-beds of the 



Walla Crags, a little to the north, are some of the 



ancient volcanic material which was emitted from 



this vent. I do not say that this old centre, near which 



