D. Forbes— On Volcanos. 327 



one or other favourite doctrine, uniformitarian or cataclysmic, 

 whichever may for the moment be most in vogue. 



British geologists of late years, all but ignoring the action of 

 internal forces, have striven to account for everything in the shape 

 of external configuration or scenery by the action of water in its 

 different forms of rain, rivers, the sea, or ice ; and, instead of 

 taking a broader view of the geological features of the land as a 

 whole, may be reasonably accused of allowing themselves to be far 

 too much influenced in their deductions by purely local circum- 

 stances at home. 



The most prominent features in the scenery of a country must be 

 its mountains, and it is well known, not only that many even of the 

 most lofty mountains in the world are actually volcanos, but also 

 that the greater number of the others, even in the British Isles, are 

 in major part built up of or founded on eruptive rocks, the product 

 of the volcanic and cataclysmic activity of former periods ; whilst 

 the countless faults and dislocations of the strata, and the upheaval 

 of vast tracts of country everywhere seen, testify to the magnitude 

 of the results effected by those forces which operate from within the 

 earth itself. 



In answering the question, therefore, as to which of these forces 

 has played the most prominent part in determining the external 

 configuration of the earth, the unbiassed geologist must necessarily 

 grant the first rank to the internal volcanic or catalysmic agencies, 

 since had it not been for their operations, our globe would still have 

 remained a comparatively smooth sphere, surrounded by its ex- 

 ternal envelope of water, with no visible land for the rivers to 

 traverse or the rain and ice to disintegrate and wear away ; in fact, it 

 was only after the internal agencies had produced their effects that 

 the external forces were called into play, and then became the great 

 agents in modifj'-ing the outlines of our earth to their fullest extent. 

 When all the facts are taken into due consideration, it must therefore 

 assuredly be admitted that the wonderful changes which now take place 

 and have been effected in the physical geography of the world, have 

 resulted from a combination of two great but most opposite agencies, 

 the internal and external, igneous and aqueous, cataclysmic and 

 uniformitarian, or by whatever other names they may respectively be 

 called ; and in considering this subject the student should always be 

 prepared to admit what I have elsewhere insisted upon, that " all 

 the phenomena of nature may be effected by a combination of more 

 forces, and that the same identical phenomena may at times be the 

 result of agencies totally different from those which at other times 

 may have given rise to them." 



The study of volcanic phenomena presents a wide and interesting 

 field for exploration, for as yet our knowledge of the subject is 

 lamentably defective ; to follow it up, however, the student should 

 work out a path for himself, taking advantage of every new means 

 of research placed in his hands by the advance made by the collateral 

 sciences, and steering clear of all schools or preconceived notions. 

 Schools in science are what parties are in politics ; the " follow-my- 



