896 
LIMESTOIfE or PEXAS KEGEAS. 
as subordinate to tlie conglomerate (erideutly of tertiary 
formation) of the Barigon and of the mountain of the 
oastle of Cumana, because a little to the iiortti of that castle 
I had found shelves of hardened clay containing lamellar 
gypsum inclosed in the tertiary strata. I believed that the 
muriatiferous clay might alternate with the calcareous conglo- 
merate of Barigon; and near the fishermen’s huts situated 
opjjosite Macauao, conglomerate rocks appeared to me to 
pierce through the strata of clay. During a second excur- 
sion to Maniquarez and the aluminiferous slates of Cliapa- 
rnparu, the connexion between tertiary strata and bituminous 
clay seemed to me somewhat problematical. I examined 
more particularly the Penas Negras near the Cerro de la 
Vela, E.S.E. of the ruiued castle of Araya. The limestone 
of the Penas is compact, bluish grey, and almost destitute 
of petrifactions. It appeared to mo to be much more ancient 
than the tertiary conglomerate of Barigon, and I saw' it 
covering, in concordant position, a slaty clay, somewhat 
analogous to muriatiferous clay. I was greatly interested in 
comparing this latter formation with the strata of carbu- 
retted marl contained in the Alpine limestone of Cumanacoa. 
According to the opinions now most generally received, the 
rock of the Penas Negras may be considered as representing 
muschelkalk (limestone of (xottingen) ; and the saliferous 
and bituminous clay of Araya, as representing variegated 
sandstone ; but these problems can only be solved when the 
mines of those countries are worked. Those geologists who 
are of opinion that the gem-salt of Italy penetrates into a 
stratum above the Jura limestone, and even the chalk, may be 
led to mistake the limestone of the Penas Negras for one of 
the strata of compact limestone without grains of quartz 
and petrifactions, which are frequently found amidst the 
tertiary conglomerate of Barigon and of the Castillo de 
Cumana; the saliferous cla}' of Araya would appear to them 
analogous to the plastic clay of Paris,* or to the clayey 
shelves (dief et tourtia) of secondary sandstone with lignites, 
containing salt-springs, in Belgium and Westphalia. How- 
ever difficult it may be to distinguish separately the strata 
of marl and clay belonging to variegated sandstone, muschel- 
* Tertiary sandstone with lignites, or molassus of .Argovia. 
