82 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 6G. 



The asbestiform hornblende definitely underlies laumontite and 

 stilbite in one specimen, but on another, fibers seem to penetrate 

 albite crystals, and in still another it appeared to rest upon prehnite. 

 Fibers of hornblende of this type were also seen inclosed in albite in 

 a thin section of the albitic pegmatite and it may precede albite in 

 formation or, more probably, its deposition extended over a consid- 

 erable range. 



Epidote of the hour-glass type was seen imbedded in chlorite in 

 asbestiform hornblende, and in prehnite, so that it is apparently con- 

 temporaneous with all of these. Prismatic 

 crystals associated with the axinite are about 

 contemporaneous with the latter and the 

 accompanying hornblende. 



Axinite was found in circumstances which 

 indicate it to be later than diopside, con- 

 temporaneous with hornblende and epi- 

 dote and earlier than apophyllite. 



Quartz was seen in only one specimen 

 where it was later than chlorite and dis- 

 tinctly earlier than datolite. 



Prehnite is apparently about contempo- 

 raneous with the last of the epidote and is 

 earlier than some datolite and later than 

 other datolite crystals, on which it forms an 

 overlying crust. This is considered to indi- 

 cate two generations of datolite. 



Datolite has been mentioned in its rela- 

 tion to prehnite. It was distinctly earlier 

 than stilbite. 



Chabazite occurred only on joints and 

 was not associated with any earlier mineral, 

 but is distinctly older than the overlying 

 stilbite. 



Stilbite is clearly younger than chabazite 

 in some specimens, and older than laumon- 

 tite in others. It was seen to be younger 

 than datolite and prehnite. 

 Laumontite is definitely younger than stilbite and as definitely 

 older than apophyllite. 



Opal (hyalite) is known only to be older than calcite. Its placing 

 in the table is thus arbitrary. 



Apophyllite is definitely younger than stilbite and laumontite, and 

 is clearly older than calcite which often forms pseudomorphs after 

 apophyllite crystals. 



Calcite is, so far as observed, the youngest mineral of the veins. 



Fig. 30. — Apophyllite from speci- 

 men OF Merrill and Wherry 



SHOWING TWO prisms, PYRAMID 

 AND BASE. 



