102 Dll BOUE' ON THE GEOGNOSY OF GERMANY. 
known to repose upon greyvvacke, and to be covered by it, 
— or, if this be denied, which are situated in greywacke. 
The granites of the Hartz, of the Thuringerwald, of 
Westmorland, of the Criffel, the granite near Loch Ken, 
&c. must be arranged here. 
A pecuharity which these granitic masses have, is to be 
often surrounded, in part, or in whole, with peculiar ano- 
malous rocks called Hornfels in the Hartz, and varieties of 
gneiss in Scotland. These last rocks are intermixed with 
the true greywacke, and pass into it. 
To these crystalline rocks succeed great deposits of 
porphyiy. These porphyries, in some countries, form 
a kind of series of alternating masses with the greywacke, 
as in Cumberland, and in the Fichtelgebirge, where 
the Felspathic Breccias or Tuffs are particularly very re- 
markable. In other countries, the porphyries seem to have 
appeared later, or not to have had that facility of alternat- 
ing with other rocks ; and hence they rise in the form of 
immense massive hills, as in Schemnitz, Kremnitz, and in 
many parts of Transylvania, of the north of Germany, and 
of the middle of France. 
In many countries, the porphyries occur in great masses, 
veins, or even in beds, in the old red sandstone (Silesia). 
But their appearance in the middle of the coal formation is 
the most interesting, because in that case we have been 
enabled to trace their origin. Near Halle, for instance, 
where such an occurrence takes place, the porphyries ap- 
pear in beautiful domes, like the Fuy de Sarcouy, in Au- 
vergne, v^^hich pass through or under the coal-formation, 
while another portion evidently extends itself above the 
arenaceous deposit. 
It is also curious to observe, in the neighbourhood of 
these porphyries, the great disturbances of the strata, the al- 
teration of the coal, and the great bodies of singular anoma- 
