312 J. W. Judd—On Volcanos. 



ill the surrounding areas simultaneously declining in energy, the 

 vast central volcanos becoming extinct, and the dying igneous forces 

 only making themselves felt in long trains of "puys," and finally in 

 hot springs and gaseous exhalations. But the volcanic commotion 

 around the Alpine system has not yet wholly subsided, and it may 

 be regarded as almost equally certain that the oscillatory movements 

 of the central mountain masses are not even yet altogether exhausted. 



We have seen how the first existence of a line of weakness in the 

 earth's crust, along what was to be the site of the future Alpine 

 chain, was betrayed by the volcanic outbursts of the Permian and 

 Triassic periods. It might at first sight appear that the renewal of 

 volcanic violence in the middle of the Tertiary period would take 

 place on the same line. But when we reflect on the enormous 

 thickening of the crust which had been eifected along this line, 

 owing to the formation of the geosynclinal and the accumulation of 

 such an enormous mass of sediments, as well as on the strengthening 

 of that part of it by its being crumpled together and converted into 

 crystalline rock, it will be clear that the lines of weakness liable to 

 yield to the volcanic forces, and so to produce eruptive fissures, will 

 no longer be situated in the axis of the synclinoriwni (as Dana calls 

 the crushed and upheaving geosynclmal) , but rather at lines of junc- 

 tion of this thickened and strengthened mass with the surrounding 

 normally developed series of stratified rocks. 



Now it is just at such points, and indeed all around the central 

 masses of the Alps, and of its several ramifying chains, that the 

 volcanic action of which we have spoken has been manifested. It 

 would require a treatise to describe the varying manifestations, the 

 history of the gradual appearance, of the attainment of its grand 

 climax of violence, and of the slow decline and gradual extinction of 

 this belt of fire which surrounded the Alpine system during the 

 period of its great and final stage of ujoheaval. In the concluding 

 chapter of this series we shall not be able to attempt more than to 

 sketch in its barest outlines the main features of this remarkable 

 history. 



On one point, however, we turn to this history with particular 

 interest, for in it, if anywhere, the geologist may perhaps hope to find 

 the solution of a problem of the highest importance. I allude to the 

 question as to what are the characters of the initiatory stages of the 

 manifestations of volcanic violence in a district The age of man, or 

 even the duration of human history, is as nothing in comparison 

 with those periods with which the geologist is called upon to deal. 

 By direct observation we can accomplish nothing, for even the 

 smallest cycles of geological change are not completed within the 

 periods dealt with by our limited experience or contracted records. 

 Doubtless in some parts of the globe the seeds of the volcanic 

 disease in the earth's crust are even now beginning to make them- 

 selves felt by premonitory symptoms ; but how are we to recognize 

 these as such, seeing that we shall not live to witness the climax of 

 the attack ? It is clear that our only hope of learning the nature 

 and characteristics of the first symptoms of a volcanic outbreak on 



