FENNER, THE WATCHUNG BASALT 145 



forms of basalt, and showing apparently the complete removal of iron and 

 magnesia compounds. The inference is that in the channels in which cir- 

 culation was most free, the waters were too dilute in iron and magnesia 

 for the deposition of these minerals, and it was only where the circulation 

 was more obstructed and therefore slower, and where a supply of iron and 

 magnesia was at hand in the less altered basalt, that these compounds 

 were deposited. 



The manner in which the amphibole was removed by dilution of the 

 solutions appears in slide 108. The bundles of acicular fibres are losing 

 their characteristic euhedral terminations and appear as small masses 

 with irregular outline. There is no indication of alteration products, and 



Co /c //e p^ /e -gre e. n 



BaTo/lfe 



Sf^/i/fc 



Co/or /ess- 

 ''/f/n^/i/6o/t 



azlie. 



Fig. 1??. Association of amphibole, datolite. chabazite. stilbite and calcite. The 

 amphibole shows both green and colorless varieties. Datolite shows corro- 

 sion at contact with zeolites, chabazite is cut by veinlike stilbite, and gran- 

 ular calcite replaces all. X 32. Slide 108. 



it appears as if the amphibole were simply being dissolved out. Datolite 

 and heulandite are the associated minerals. 



Variety 4. Under certain circumstances, the amphibole appears to 

 suffer a diminution in iron content without destruction of the crystals, 

 perhaps altering in the direction of tremolite. This is observable in 

 several slides. The green and brown pleochroic colors have practically 

 disappeared. The crystals retain their outline and fresh appearance, but 

 are colorless or show a very faint tinge of green. A group in slide 108 

 (fig. 15) shows transitions between individuals which are decidedly pleo- 

 chroic and those in which the green is barely perceptible. Datolite is 

 associated, but zeolites and calcite are the prominent minerals present. 



