562 Geological Society: — Mr. J. W. Judd on the Ancient 



Lake, which was not previously in existence. The general results 

 of this investigation are as follows : — After the last important dis- 

 turbance of the prae-Permian rocks,, North Wales was carved slowly 

 and by subaerial agencies into its present mountainous form chiefly 

 between Permian and Preglacial times. The work of the glaciers 

 of the latter period somewhat deepened, widened, smoothed, and 

 striated the minor outlines of the mountains and valleys, and exca- 

 vated many rock-bound lake-basins, but did not effect any great 

 changes in the contours of the country. A minor submergence of 

 part of Britain during part of the Glacial epoch produced no im- 

 portant effects on the large outlines of the rocky scenery ; and the 

 effects of subaerial waste subsequent to the Glacial epoch have been 

 comparatively small. 



3. " On the Ancient Volcano of the District of Schenmitz, Hun- 

 gary." By John W. Judd, Esq., F.G.S. 



The old volcanoes of Hungary have long been known to present 

 some very interesting illustrations of the relations between the 

 igneous rocks erupted at the surface, and those which have con- 

 solidated at a considerable depth beneath it. The district in which 

 these phenomena can be best studied is that of Schemnitz ; but 

 although this area has been very carefully mapped and explored by 

 a number of able investigators, the greatest diversities of opinion 

 still exist concerning the relations of certain of the rock-masses 

 exposed within it. 



Over an area nearly fifty miles in diameter enormous accumu- 

 lations of andesite and quartz-andesite lavas and agglomerates have 

 been erupted, these now forming a group of mountains rising from 

 3000 to 4000 feet above the sea-level, and culminating in a great 

 ring of precipitous heights overlooking a depressed central area of 

 oval form, the site of the famous mining towns of Schemnitz, 

 Kremnitz, and Konigsberg. In the midst of this depressed central 

 area there occurs a considerable development of rliyolitic lavas and 

 tuffs, and more scattered outbursts of basalt. From the magnificent 

 floras associated with the various volcanic tuffs, we know that the 

 andesitic rocks were erupted during the earlier portion of the Upper 

 Miocene period, and the rhyolitic towards its close, while the basalts 

 are probably of as late date as the Pliocene. 



Besides the rhyolites and basalts, however, there are certain 

 other rocks exposed in the central area of the Schemnitz district, 

 the relations of which it is very difficult to understand. These 

 consist of (1) strata of Lower Trias and Nummulitic age, through 

 the midst of which the volcanic outbursts have evidently taken 

 place ; (2) masses of highly metamorphic rocks, including quartzites, 

 crystalline limestones, various schists, gneiss and aplite ; and (3) 

 undoubted eruptive rocks, which have usually been called " syenite 

 and granite," but for which the names of " diorite and quartz- 

 diorite " would perhaps be more appropriate, inasmuch as the pre- 

 vailing felspar in them is always a plagioclase variety. 



By Beudant and other early writers the andesitic lavas were 



