224 Professor Hoffmann on the Geological Investigations 



in the Alps are ruptured and changed by the melaphyre, as 

 belonging to the middle period of the secondary series, with- 

 out, however, great weight being attached to this important cir- 

 cumstance. But afterwards it v/as proved, that this limestone 

 is actually of younger formation than was imagined, and that 

 it belongs to the period of the chalk and its older adjoining 

 formations. Hence the elevation which had taken place in 

 the Alps is comparatively a very new event, and hence the 

 period of its occurrence can no longer be applied to the above- 

 mentioned elevations of the mountains of Northern Germany ; 

 for the porphyries which have there come into operation, were 

 formed at a comparatively much older date. In the north of 

 Germany we have no porphyry whose date is more recent than 

 the rothe Todte. 



Further, it has not yet been established by direct observa- 

 tion, that the red and black porphyries of Northern Germany 

 exhibit the same marked separation which is so distinctly ap- 

 parent in Southern Tyrol. In the neighbourhood of the 

 Hartz, and of the Tliuringer JFald, on the river Nahe in 

 lower Silesia, and at Meissen, no undoubted breaking through 

 of the red porphyry by the melaphyre has been ascertained, 

 whether it be that, from the want of sections in these less ex- 

 posed and less elevated rocks, such phenomena escape the ob- 

 server, or that there the two porphyries occur as members of 

 one and the same great and contemporaneous formation, which 

 presents different characters at different places. 



At the Lake of Lugano, likewise, the relations of the two 

 porphyries in the region of the Alps have given rise to doubt, 

 and all observers have not believed themselves justified in 

 participating in the view which Buch has given of that clas- 

 sical locality.* It would rather appear, from my own obser- 

 vations, that, vice versa, the red porphyry forms veins in the 

 black, and that both are of older origin than the limestone, 

 which, therefore, has, without their operation, been converted 

 into the remarkable dolomite of Monte Salvatore, 



♦ Every geological traveller to the lovely and interesting shores of the 

 Lake of Lugano has experienced the value of Von Buch's map which ac- 

 companies liis account of that spot. — Edit. 



