ofihi Amphibole <md Pyrosoen* groups. 



363 



gregate aearesl the large crystal extinguish to tin- righl oi 

 the vertical axis of the latter. 



Prom the relationships observed In studying several sections 

 of this poek the writer concludes that the actinolite of the orya 

 taJ shown in fig, 5 replaces primary brown hornblende, and 

 that the dark chestnut-brown portion is an added growth 

 Taken by themselves the Bharp boundaries might well be con- 

 sidered as indicating original intergrowths of three varieties. 

 The probable character of the added brown material will be 



spoken of below. 



The augite of this dike rock is more strongly attacked than 

 the hornblende by that decomposition which has resulted in 



the production of calcite and quartz, but it gives way to the 

 influences which have produced the blue amphibole far less 

 readily. Vet alteration very similar to uralitixation may be 



<;. 



seen progressing from the irregular fissures in the augite. 

 The fibrous product is sometimes pale green and sometimes 

 blue, and whenever the latter is developed so as to give homo- 

 teoua optical action it can be seen to be identical in its prop- 

 erties with that form already described, while the green is 

 probably actinolite. 



The blue amphibole is also added to augite grains, as illustra- 

 ted in figure 6. Such occurrences are comparatively rare but 

 they are sometimes very distinct. In the case figured the augite 

 is twinned parallel to ooPoo and the particles of blue am- 

 phibole added to the two parts are correspondingly orientated, 

 as is also a small fibrous mass within the augite grain. Nearly 

 every grain of hornblende and many of augite exhibit the blue 

 amphibole regularly implanted upon or replacing the primary 

 mineral in the wavs represented by the figures. Fissures trav- 



