,522 EGG. GEOLOGY. 



tains no imbedded minerals; those zeolites and chalce- 

 donies which are found dispersed near the Scuir being 

 derived from the trap rocks associated with it. The 

 nodules of chalcedony are the most abundant, and among 

 these I procured a specimen of that onyx so deservedly 

 in esteem among sculptors for works in cameo. The 

 laminse are parallel and of the most decided opposition, 

 the one being brown the other white, with the line of 

 separation between the colours decidedly marked. 



In a slight notice on this island in the second volume 

 of the Geological Transactions, I mentioned that this rock 

 rested on a marie, and that again on a sandstone. This 

 is an error which the further clearing away of the soil 

 since that time enables me to correct. The " marie" is a 

 mixture of limestone, clay, and sand, containing nodules 

 and veins of rude quartz, but there is reason to suspect 

 that it is a large nodule entangled between the porphyry 

 and the subjacent mass, or else belonging to the latter, and 

 not a continuous bed. This mass is a conglomerate con- 

 sisting of small and large fragments of red sandstone, trap, 

 and silicifted wood, imbedded in a basis of trap ; a sub- 

 stance already described as occurring in the island of 

 Canna. In other places the Scuir may be clearly seen 

 resting on the same trap with which it alternates, and 

 thus forming, as I before remarked, the uppermost rock of 

 this interesting island. 



