324 J. W, JTTDD ON THE ANCIENT VOLCANO OF 



different from that of the surrounding stratified rocks to admit of 

 any such interpretation, but the final product of metamorphism of 

 the Triassic rocks is actually seen in the aplite — which must have 

 been reduced to a liquefied condition, and graduates most insensibly 

 through the gneissose and schistose rocks into the sedimentary 

 masses ; and yet the distinction in character and composition between 

 the aplite and the dioritic rocks is most clear and unmistakable. 



(4) The mineral veins of Hungary and Transylvania, with their 

 rich deposits of gold and silver, cannot be of older date than the 

 Miocene, while some of them are certainly more recent than the" 

 Pliocene. Hence these deposits of ore must all have been formed at 

 a later period than the clays and sands on which London stands ; 

 while in some cases they appear to be of even younger date than the 

 gravelly beds of our Crags ! 



EXPLANATION OF PLATE XX. 



In this Plate the same plan of colouring has been adopted as in those illus- 

 trating the paper " On the Ancient Volcanoes of the Highlands," published in 

 vol. xxx. of this Journal. The distinctive chemical character of the several 

 volcanic rocks is indicated by different colours — blue representing the basic 

 lavas and red the acid, while the varieties of intermediate composition are di- 

 stinguished b}- shades of purple. The depth of tint in each case indicates the 

 more or less highly crystalline character of the several rock-masses; thus dark 

 purple represents the granitic andesite, or diorife, and fainter tints the ordi- 

 nary andesitic lavas. The same plan of colouring is adopted both in the map 

 and section. In the former the broken line shows the approximate boundary 

 of the great " Oaldera " to which the crater of Schemnitz was reduced by pro- 

 longed denudation ; the continuous line is the direction of the section below, 

 which is drawn on a true vertical and horizontal scale, twice as great as that of 

 the map. The scale of the map is about one inch to six English miles ; that 

 of the section one inch to three miles. 



Discussion. 



The President (Prof. Duncan) remarked that it was curious to 

 note that the same volcanic rocks had been ejected in past 

 times as were being thrown out at the present day ; whilst, on the 

 other hand, in two neighbouring districts volcanic rocks of com- 

 pletely distinct natures were being ejected at the same time. He 

 did not consider plants to be a safe guide to the age of beds, as 

 they are known to extend through long periods. 



The Duke of Argyll expressed his personal thanks to Mr. Judd 

 for the light he had thrown on volcanic rocks, more especially those 

 of Scotland. The most important point was the identity of rocks 

 hitherto considered distinct. In the Isle of Mull granite had been 

 found passing insensibly into porphyritic and volcanic rocks. 



Mr. W. W. Smyth said that formerly the rocks of this district were 

 divided into metalliferous and non-metalliferous. In going over this 

 spot with Yon Hauer and others, he had pointed out Nummulites at 

 Eisenbach, and had then maintained that the crystalline rocks there 

 were metamorphosed Nummulitic Limestone. A map of part of 

 this region, which he had drawn at thai time, agreed in most re- 



