38 



University of California. 



[Vol. i. 



partly replaced by calcite. Certain other nearly colorless, grayish 

 decomposition products of an indeterminate character also appear 

 in the same slide. These polarize as an aggregate. Certain speci- 

 mens from another locality on the shore are interesting as showing 

 various stages of decomposition of iddingsite to serpentine (?). The 

 alteration seems to begin in the center most commonly. Crystals 

 may be observed with idiomorphic boundaries, which in their central 

 portions consist of a greenish fibrous mineral. This green product 

 is very feebly polarizing, and sometimes is practically isotropic. In 

 some cases it polarizes as an aggregate. The peripheral portions of 

 the same crystal are normal iddingsite. In other cases the entire 

 phenocryst is replaced by the green material. In some cases, also, 

 the iddingsite has acquired a green color without losing its char- 

 acteristic optical properties. There is also a varying proportion of 

 the green matter in small patches or elongated shreds scattered 

 through the ground-mass. 



A chemical analysis of a representative sample of the carmeloi'te 

 from Sunium Point gave the following results: — 



Si o. 2 



52.83 



Ti 2 



trace 



Al a 3 



17.67 



Fe 2 O, 



7.50 



Fe O 



1.68 



Ca O 



7-35 



Mg O 



2.47 



K, 



2.52 



Na, 



6.61 



Ignition 



2.32 





100.95 



Sp. g. 



2.80 



On the shore east of Sunium Point the same rock presents 

 other facies. It is here thinly bedded, shows in places a con- 

 torted structure, due to viscous flow, has intercalated agglom- 

 erates, and is strongly vesicular or amygdaloidal. This amygda- 

 loidal facies differs from that of Sunium Point in its microscopic 

 aspects in the preponderance of glass in the ground-mass. The 



