33S EXTINCT VOLCANO IN ElllTAlN. 



of immense magnitude. The mountain alluded to is Cader 



Idris, situate in* the. county of Merioneth, which in point of 



size is esteemed the most considerable in the principality of 



Wales, Snowdon alone excepted* 



First noticed The remarkable appearance of this, stupendous mountain 



J^ r ' no * attracted the attention of Mr. Donovan about seven years 

 vuii seven y eurs 



a «°- ago. He was then led to consider from a variety of circum- 



stances, that iLe original form of the mountain must have 

 undergone very material alteration,, occasioned as he con- 

 ceived by the powerful effects of the volcanic explosion ; but 

 his remarks were not .sufficiently precise to authorise the as- 

 sertion. Since that period he has examined the mountain 

 in a less cursory manner, more especially in the summer of 

 1307, when he was at .full leisure to devote some time to this 

 interesting subject of inquiry, and his observations in the 

 latter instance tend entirely to confirm the idea iir&t sug- 



Proofsinvol- gested. In support of tiiis opinion Mr. Donovan has now 



came produc- a( Jd e d to h\ s mU seum abundant examples of different kind* 

 twrib collected r 



there m ISO 7. °f lava, pumice, and other volcanic matters of the most une- 

 quivocal character, collected by himself from the sides and 

 base of the mountain ; and also a suite of the remarkable and 

 singularly formed columnar crystals of basalt, that are scat- 

 tered in profusion about the loftiest summit, and cliffs sur- 

 rounding the crater. 

 Appearance of The general aspect of this crater is exactly that of mount 

 the crater. Vesuvius, except that one of its sides is broken down, by 

 which means the abyss of this funnel-shaped excavation is 

 Wiore completely dis^lo;-**! than in the Vesuvian mountain ; 

 and it this side of Cader ldris which affords the most illus- 

 trative examples of porous stones, these forming immense 

 beds on the declivities a few inches only in many instances 

 below the surface of the, eaith. A number of these porous 

 . stones lately found in this spot by Mr. Donovan exhibit evi- 

 dent marks of strong ignition and' vitrification, some are re- 

 duced to the state of slags, while others have all the cel£ular 

 1 lightness of pumice. 



appearance and 



V» 'jthout entering upon any discussion as to the relative 



formed by an merits of the neptunian and vulcanian theories, it must be 



2 er 1 ™ admitted, that the agency of water might have contributed 



materially to affect those changes in the primitive form of tfie 



Cader 



