214 J, W. Judd — On Volcanos. 



by the opening of a number of sporadic vents in the same district. 

 We have also pointed out that both to the eastward and westward 

 of the region which we have been more particularly describing, and 

 evidently constituting part of the same linear series of contempo- 

 raneous eruption, we find, wherever the superincumbent rocks have 

 been removed by denudation, similar evidences of volcanic action 

 taking place prior to the formation of the Alpine system. 



In concluding this chapter we shall enumerate and very briefly 

 describe the principal exposures of the products of this old line of 

 volcanic action. 



On the shores of the Lake of Lugano there occurs a tract occupied 

 by igneous rocks, which are shown, by their relations to the sedi- 

 mentary masses of the district, to have been erupted after a portion of 

 the Permian strata were deposited, and before the great mass of the 

 Triassic rocks were formed. These igneous rocks appear to consist 

 of great masses of quartz-porphyry, very similar to that of Botzen, 

 with smaller and subordinate outbursts of porphyrite and melaphyre. 

 Some masses of truly granitic rock appear in the same district, which 

 may also perhaps belong to the same age. The general resemblance 

 of these rocks of Lugano and Ticino with those of the Southern 

 Tyrol is very striking ; and, were we able to remove the masses of 

 younger strata which cover almost the entire country between these 

 two districts, we should probably find the two areas of igneous rocks 

 to be parts of the same continuous series. Indeed, at more than 

 a dozen intermediate points, the widely-spread Permian quartz- 

 porphyries have been detected in the bottoms of deep valleys, and 

 wherever the newer rocks have been cut through by denudation. 



Passing eastward from the grand exposures of the pre-Alpine 

 volcanic rocks, we find them again making their appearance in the 

 country about Eaibl in Carinthia. The beautiful red quartz -porphyry 

 of this locality (containing 76 per cent, of silica) is associated with 

 volcanic tuffs, and rocks of more basic character; there is the 

 clearest evidence that these rocks were erupted at the same period as 

 those of the Southern Tyrol and Lugano. Isolated exposures of the 

 same rocks have also been detected at a number of other points in 

 Carinthia. 



Still farther in the same direction, and where the Alpine chain sends 

 off its two great eastern branches, namely, the Carpathians stretching 

 to the north-east, and the Julian Alps extending towards the south- 

 east, we find masses of eruptive rock of the same age as those we 

 have been noticing. Such are the various igneous masses of the 

 Island of Lissa and other points in Dalmatia, and the melaphyres of 

 "Waag, which are of Permian age, with others at several points in 

 the Carpathians and Transylvania, which were erupted at intervals 

 during the Trias and part of the Lias period. The occurrence of all 

 these igneous masses would seem to indicate that, not only was there 

 made manifest at the close of the Permian epoch the existence of a 

 line of weakness in the earth's crust, nearly coincident with the great 

 central Alpine mass, but that the principal fractures radiating from 

 it must have been already even at this early period determined. 



