634 



of that castle I had found shelves of hardened 

 clay *, containing lamellar gypsum inclosed in 

 tertiary soil (Vol. iii, p. 11). I believed that 

 the muriatiferous clay might alternate with the 

 calcareous agglomerat of Barignon ; and near 

 the fishers' huts situated opposite Macanao, 

 agglomerate rocks appeared to me to pierce 

 the strata of clay. In a second excursion to 

 Maniquarez and the aluminiferous slates of 

 Chaparuparu (Vol. vi, p. 93), the connexion be- 

 tween tertiary soil and bituminous clay, seemed 

 to me somewhat problematical. I examined 

 more particularly the spot of Penas negras near 

 the Cerro de la Vela, E. S. E. of the ruined 

 castle of Araya. The limestone of the Penas\ 

 is compact, of bluish grey, and almost desti- 

 tute of petrifications. It appeared to me to be 

 much more ancient than the tertiary agglome- 

 rate of Barignon, and I saw it covering in con- 

 cordant position, a slaty clay, somewhat ana- 

 logous to muriatiferous clay. I had a pleasure 

 in comparing this latter formation with the 

 layers of carburated marl contained in the al- 

 pine limestone of Cumanacoa. According to 

 the geognostic ideas that are now the most 

 generally spread, the rock of Penas Negras 

 may be considered as representing the musclnel- 



* Not muriatiferous, and without petroleum ? 

 t See above Per. Nar. Vol. ii, p. 264 to 269. 



