Relations of Trap-llocks with Ores of Copper. 17 



cuous, because their blunted forms present only gentle slopes 

 covered by an active vegetation. But they can be studied in 

 numerous excavations, where we perceive the massive struc- 

 ture of the greenstones, a structure often globular, so as to 

 present mammelated sui'faces. 



The tissue of these rocks is generally homogeneous and 

 compact ; their colours deep, often ochreous on the surface, 

 but greenish in the fractures which reach the unaltered rock. 

 These appearances, moreover, are subject to variations suffi- 

 ciently indicated by the multitude of names applied to them, 

 such as greenstone, traps, variolites, amphibolites, diorites, 

 &c. If we look for analogous formations, these rocks can- 

 not be better compai-ed than with those, which, in fact, bear 

 the same names in the group of the Harz mountains. 



If we study attentively some <5f the principal trap masses, 

 we observe that the central pai't is pretty constant in its 

 chai'acters ; it is a green rock, homogeneous and compact, the 

 true type of greenstone. The variations which have caused 

 so many different names to be applied to it, occur principally 

 towards the exterior zones ; a condition which we have pointed 

 out in the serpentine masses of Tuscany, and which likewise 

 exists in the greenstone of the Harz. If we examine the 

 true rocks of contact, we shall find them exhibiting charac- 

 ters still more complex, but which always remind us of some 

 of those of the trap type. 



These rocks of contact are designated at Nassau by the 

 general denomination o^ schahtein. 



It is very difficult to define schalstein. It is most fre- 

 quently a compact and lithoid rock, green or reddish, much 

 rent, especially in the general direction of the stratification ; 

 some varieties are even slaty, others are brecciform and 

 massive. The red colour of schalstein sometimes becomes 

 very deep, and it contains, occasionally, conformable beds 

 of red peroxide of iron. Lastly, the variolitic amygdaloids, 

 with calcareous nodules, also form part of the schalstein, and 

 develop themselves more especially in the parts of the loca- 

 lity where the Devonian limestones exist. 



The schalstein has long attracted the attention of those 

 who have studied the rocks of Nassau. Becher, Walchner, 



VOL. .\LVII. xo. XCIII. — .lUI-V 1849. B 



