174 ANNALS NEW YORK ACADEMY OF SCIENCES 



stiffened into a glass and was subsequently set free by the decomposition 

 of the latter by solutions. 



Apophyllite is the first mineral met in the series in which potash plays 

 a prominent part in the formula. The source of the potash, however, is 

 not far to seek. The analyses of typical examples of basalt given on an 

 earlier page show potash to be universally present, and while the earlier- 

 formed minerals are essentially soda and lime compounds, some of them 

 undoubtedly carried a certain amount of potash replacing a portion of 

 the soda. 



Chlorite 



Chlorite is almost universally present. In those slides, however, in 

 which the minerals are prevailingly of the first period of alteration, the 

 quantity of chlorite is so small as to lead to the suspicion that it does not 

 properly belong here. Throughout the second period, however, it seems 

 to have been developed in considerable quantity and to have extended 

 through the third period likewise. 



Considerable variation in appearance and properties is observable, and 

 a number of members of the chlorite group may be present, but it has not 

 been considered a favorable opportunity to make a detailed study to deter- 

 mine this. The color varies from bright emerald-green to pale yellowish 

 green, or almost colorless. Birefringence is never strong, but varies from 

 moderate to almost isotropic. The general habit is aggregates of minute 

 scales, but it may develop in fairly large blades, especially when in 

 nodules from alteration of resorbed olivine. There is quite a tendency 

 to become segregated in definite areas or to migrate into cracks. 



The constant tendency for magnesium and iron to be leached out 

 throughout the whole process of alteration has been mentioned in several 

 places. It was observed that the green amphibole was usually found in 

 close association with the less altered basalt, while in the less obstructed 

 channels it was seldom found. This relation is probably even more 

 characteristic of chlorite. One exception has been noted, however. It is 

 not uncommon to find vugs lined with calcite crystals which show small 

 spheroidal groups of chlorite perched upon them. 



Green amphibole is often found in the same slides as chlorite but 

 seldom in intimate association. There is little to indicate an alteration 

 of one into the other. 



Serpentine 



The quantity of serpentine is so small as to be almost negligible. It is 

 probably present in some cases, associated with chlorite. 



