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of.a very cellular structure. About the middle of the east side of 
the great crater, it contains a very thick mass, composed of alterna- 
tions of greenish porphyry, slightly lamellar in structure, and of red 
ochreous clay. Near the northern pass Mr. Burr noticed a granu- 
lar rock, or volcanic breccia. The inclination of the beds is gene- 
rally 15° from the crater. . " 
Numerous perpendicular dykes intersect the volcanic rocks, and 
are harder and more compact than the beds they traverse. Small 
veins of calcedony also occur. 
Dr. Malcolmson showed Mr. Burr some specimens of black and 
green obsidian obtained on the promontory, but the conditions 
under which they exist Mr. Burr was prevented from ascertaining. 
The deposits of consolidated sea-sand occur more especially near 
the northern pass, towards the base of the volcanic ridges. The 
_ stratification is diagonal, and this arrangement Mr. Burr conceives to » 
have been produced by the drifting of opposing currents. The flat 
line of coast on the northern part of the promontory, the author 
says, is evidently a raised beach, and the consolidation of the sand he 
assigns to the action of a tropical sun upon the calcareous materials. 
_The stone incloses numerous shells and corals of species existing in 
the Arabian Sea. 
