FENNER, THE WATCHU]\G BASALT 



153 



and in the radial disposition of included dust, of a former spherulite in 

 the basalt, various occurrences of which have been described. 



In 75, there is probably a replacement of datolite by natrolite. Slide 

 108 furnishes a fine example of deeply corroded crystals in contact with 



^ Fig. 19. Replacemeut of datolite (Da) by stilbite (St). X 35. Slide 110. 



stilbite, heulandite and chabazite. Fig. 15 shows the association at one 

 point. With the datolite, a considerable quantity of amphibole is found. 

 In one or two places, the basalt is very little altered and is seen to have a 

 typically vitrophyric texture. The remnants of datolite and amphibole 



St, I hit e 



Jiatt/tte 



Ca /cifc 



Fig. 20. Swarms of corroded crystals of datolite in stilbite. X 35. Slide 83. 



show a distinct tendency to form borders to the less altered rock, while 

 the zeolites are best developed farther out. This is probably the result of 

 leaching-out of datolite where circulation was most free. 



