Lawson.] 



Geology of Carinelo Bay. 



39 



magnetite, moreover, does not seem to have been individualized, 

 but to have remained in the glass as a dusty material, rendering it 

 nearly or quite opaque. No augite was observed, and the clear 

 green varieties of the iddingsite phenocrysts are here studied to best 

 advantage. The vesicles are usually flattened in the planes of flow. 

 The amygdules consist commonly of chalcedony, calcite, and chlo- 

 rite. 



The Ravine Area. — About a mile due east of Sunium Point, the 

 seventeen-mile pleasure drive passes through a narrow ravine. 

 Along the sides of this ravine there is exposed beneath the terrace 

 formations a large oval area of carmeloi'te, which is well seen in 

 the rock cuts along the drive. The area may be so extensive as to 

 merge with the Sunium Point area beneath the newer formations; 

 but there are certain local peculiarities which suggest that it is a 

 somewhat different flow. These differences are not so pronounced 

 macroscopically as they are microscopically, owing to the vagaries 

 of weathering. Under the microscope the rock of the ravine area 

 differs from that of Sunium Point chiefly in the absence of pheno- 

 crysts of augite, the notable amount of glass, and the pres- 

 ence of iddingsite in the ground-mass in comparative abundance. 

 In some of the slides in which iddingsite is abundant, this mineral 

 assumes a habit which is not observed in the carmeloi'te from other 

 localities. The forms seen in cross section are prevalently long 

 and rectangular; and the oblong character seems to be due to the 

 excessive elongation of the crystals in a direction perpendicular 

 to the cleavage, i. e., parallel to the axis a. These crystals have 

 a bleached aspect, and are colorless ; or are clear, light greenish 

 yellow, or cloudy, brownish gray in color. The pleochroism is, 

 however, pronounced, with the same absorption formula as in the 

 normal phases of the mineral. The interference colors between 

 crossed nicols in these pale iddingsites, are brilliant green and pink, 

 not unlike those of muscovite. The cleavage is exceptionally well 

 developed. The shrinkage of the mass of the original crystal is 

 also excellently well shown in these sections by the spaces between 

 the cleavage lamellae. The only other local featureof special interest 

 presented by this mineral is its occasional occurrence as a core of 

 deep brown color surrounded by a peripheral area of light greenish 



