1848.] HAMILTON ON THE AGATE QUARRIES OF OBERSTEIN. 211 
and this place must be considered as the real centre of the agate 
trade. 
Before however describing the quarries themselves, I must briefly 
describe the geological character of the intervening country. All 
traces of stratified or sedimentary deposits cease with the conglome- 
rate which overlies the amygdaloidal rocks of Oberstem. ‘This rock 
here forms lofty cliffs, and has, at first sight, a generally greenish 
hue: it contains numerous small vesicular cavities filled with zeo- 
lites, carbonate of lime and other crystalline substances, as well as 
siliceous deposits. The matrix of the rock, however, is very com- 
pact, rather porphyritic, and of a dark brown or chocolate colour, 
and when exposed to the weathering and atmospheric influences by 
which the contents of the numerous small cavities have been decom- 
posed, assumes the appearance of a brown vesicular trap rock. The 
green hue is derived from the exposed surfaces of the imbedded 
substances. The real agates are not usually found in this amyg- 
daloid ; looking at it from a distance there is a faint appearance of 
general stratification parallel to that of the overlymg conglomerate, 
though on a nearer approach nothing of the kind is visible in the 
rock itself. 
Leaving the town of Oberstein, and proceeding westwards up the 
valley, the same greenish-brown amygdaloidal trap continues for 
some distance, but in places becomes more porphyritic or hornstone- 
like, and is studded with small agates and chalcedonic pebbles or 
nodules, which appear sometimes to run in lines not unlike flints in 
the chalk formation, though the nodules are generally at a greater 
distance from each other. 
Proceeding further up the valley, these porphyritie and amygda- 
loidal rocks are underlaid by others of a more compact and more 
decidedly igneous character; they are, first, a pale reddish por- 
phyry, very close-grained and compact, with small grains of a white 
opake substance, or of a transparent. siliceous appearance, im- 
bedded im a pale red paste; secondly, a brown, chocolate-coloured, 
compact, homogeneous rock, resembling hornstone in its fracture ; 
while, thirdly, still further to the N.W. or W., these rocks are suc- 
Quarries. 
Agate 
Oberstein 
— 
Nahe Valley. 
— OOO Oe 
_- 
— ees 
| 
y) 
eS VY d e 
W.N.W. E.S.E. N.N.W. S.S.E. W.N.W. E.S.E. 
a. Red conglomerate. d. Greenstone. 
6. Green amygdaloid. e. Trap rock with agate nodules. 
e. Porphyry. 
ceeded by a highly crystalline greenstone. The precise points of 
junction between these different rocks are much obscured by the 
fallen detritus of the hills, and could not be clearly made out during 
my hasty examination, but the greenstone occurring near the middle 
of the valley, and the furthest removed from the point from which 
R 2 
