/. W, Judd — On Volcanos. 341 



which contain the valuable masses of fuel so characteristic of the 

 formations of this period. The effects produced by the conflicting 

 action of movements of opposite character, resulting from the 

 gradual breaking up and destruction of the great Alpine geosyncUnal, 

 appear to me to be just such as would result in the formation of 

 those vast lakes, either connected with or entirely separated from 

 the sea, which characterize the Oligocene period. Such lakes, by 

 the accumulation of sediments in them, would be converted into 

 alluvial plains, that, after supporting luxuriant forests or vast peat- 

 mosses^ appear ta have been again depressed and re-converted into 

 receptacles for sedimentary deposits ; the same operation being 

 repeated again and again through a thickness of thousands of feet, as 

 is illustrated by the basins of Brown Coal in Northern Gi-ermany, and 

 the equally vast Coal-basins of the Oligocene period in Eastern 

 Europe. The duration of this well-sustained conflict between the 

 tendencies towards depression and upheaval respectively must have 

 been enormous, as shown alike by the thickness of the deposits 

 formed at certain points during the interval, and by the changes 

 undergone both by the moUuscan and mammalian faunas between 

 its commencement and termination. That the conflict terminated 

 finally in the triumph of the tendencies towards elevation is suffi- 

 ciently proved by the vast increase in the extent of the land area 

 which certainly existed during the next succeeding period, that of 

 the Miocene. Thus it is clear that the lateral thrust to which the 

 thickened masses of sediments of the Alpine line of weakness had 

 been so long subjected resulted, towards the close of the Oligocene 

 period, in a marked and general elevatory movement, succeeding to 

 the subsidences of the Secondary and Eocene periods, and the oscil- 

 latory eff*ects of the earlier Oligocene. 



No fact is now more familiar to geologists than that the areas of 

 the earth's surface in which active volcanic vents exist are usually 

 subject to elevatory movements; and it is interesting to find the 

 converse of this proposition very strikingly illustrated in the ancient 

 geological history of the Alpine system. No sooner do we detect 

 the symptoms of the long-continued movements of subsidence being 

 gradually brought to a close, than we also begin to notice the first 

 symptoms of the renewed outburst of volcanic forces, in the regions 

 where, as we have before seen, they had been so long quiescent. And, 

 as the elevatory tendencies graduall}'^ gathered strength and force, and 

 finally overcame the prolonged downward movements, so we find 

 the volcanic outbursts increasing in number and violence. Till at 

 last, at the very period when we detect in the whole Alpine system 

 unmistakable evidences of upheaving movements on the most 

 stupendous scale, we also observe in the whole of the surrounding 

 areas the clearest proof that volcanic outbursts of the most tre- 

 mendous violence were taking place contemporaneously, and build- 

 ing up cones of prodigious dimensions. Finally, when towards the 

 close of the Miocene, and through the long periods of the Pliocene 

 on to the present day, the movements of the central Alpine masses 

 became less rapid and violent, we find the volcanic manifestations 



