/. W. Judd — On Volcanos. 213 



Now the exquisite products which Nature has, at Vesuvius, ex- 

 ported from below and duly delivered at the surface, by the trans- 

 porting power of steam, may be examined by us at Monzoni, still 

 lying in the workshop in which they were elaborated. In the case of 

 "Vesuvius, volcanic explosions have brought the minerals to us, but 

 in that of Monzoni denudation has enabled us to penetrate to their 

 birthplace ; and in the very heart of this old volcano, now cold and 

 dead, the geologist may study the products of operations similar 

 to those which are doubtless taking place, far below the surface, in 

 the case of vents which we still see in activity around us. 



The various localities for the beautifully crystallized minerals of 

 Monzoni all appear to be situated at the junction of the igneous 

 rocks with the limestone masses, through which they have burst or 

 which are in some cases entangled in them. It has also been shown, 

 as indeed we might have anticipated, that the species of minerals 

 produced at the planes of contact of the limestone with the more 

 basic igneous rocks (hypersthene and diallage rock, diabase or 

 pyroxene monzonite) are different from those which have originated 

 at the junction surfaces of the more acid rocks (the Monzoni- or 

 augite- syenite). We have indicated in our list of minerals those 

 which are usually found near the masses of basic rock, and such as 

 occur in proximity to the more acid ones respectively. 



In not a few cases, as might be expected from the great age of the 

 deposits in which they lie, and the vast series of changes to which 

 they have been subjected, some of the minerals have been converted 

 into pseudomorphs. And on the same ground we may easily account 

 for the absence of all those more unstable mineral products which 

 are found at Vesuvius and other active volcanic vents. We have the 

 clearest proof that the volcano of Monzoni, and the other contem- 

 poraneous ones of the Southern Tyrol, have gone through a precisely 

 similar series of changes to that which has befallen our own old 

 volcano of Arthur's Seat, and many similar ones in Central Scotland, — 

 namely, that they have first been buried under many thousands of 

 feet of younger strata, and that subsequently, by the upheaval and 

 denudation of these, they have been once more exposed to view at 

 the surface. To a recently published memoir of vom Eath we are 

 indebted for much new and most valuable information concerning 

 the nature and mode of origin of the minerals of Monzoni. I need 

 not in this place do more than refer to the similarities of the 

 varieties and manner of occurrence of these beautiful minerals of 

 the Tyrol with those which I have described as occurring among 

 the ancient volcanos of the Highlands. 



We have now shown how, through the accidental removal by 

 denudation of the overlying rocks of the Southern Tyrol, the fact 

 has been revealed to us that during the Permian j^eriod enormous 

 masses of volcanic rock (identical in character with the modern 

 Liparites and Dacites) were erupted along a line nearly coincident 

 with that of the subsequently formed Alpine Chain ; and that these 

 grand outbursts — which led to the formation of volcanic mountains 

 at least 8000 to 9000 feet in hei2:ht — were followed after an interval 



