TIERRA DEL FUEGO. 605 
The greenstone passes into an amygdaloid. One variety of the 
latter contains thickly disseminated, small round nodules of cale spar, 
looking like pebbles, the size being a sixth of an inch or less. At other 
places, the nodules are larger and more various in size. Besides calc 
spar, they contain quartz, stilbite and datholite, the last presenting the 
radiated spheroidal forms of the variety botryolite. Stilbite also formed 
veins intersecting the greenstone, some of which, on Burnt Island, 
were two inches thick, and afforded fine crystallizations. The same 
rock contained green earth in nodules, and a greenish-black mineral 
in short, hexagonal prisms, which appeared to be another form of the 
same species. 
In addition to the minerals mentioned, epidote is also found in the 
greenstone, in minute crystals in quartz, or in veins. It is also fre- 
quent in massive forms, or occurs impregnating large masses of rock. 
It has the light pistachio-green colour characteristic of this mineral. 
Olivine was also observed in small quantities. 
Besides the greenstone, a reddish trachyte is abundant about the 
summits of some of the hills: it has the colour of a well-burnt brick, 
and is more or less vesicular. The specimens often contain distinct 
crystals of glassy feldspar and hornblende. A trachyte of a very light 
greenish-gray colour occurs in other hills, containing the same mine- 
rals disseminated in crystals. 
Specimens of rocks to the southwest of Orange Harbour were ob- 
tained by officers of the Expedition, from which it appears that the 
greenstone is associated with a green and red jasper, or intersected by 
it in veins. 
Size and Direction of Dikes.—The dikes of greenstone and trachyte 
were well exposed along the shores of the bay, and on Burnt Island. 
The following are the characters of some dikes observed on the coast, 
north of Orange Harbour. 
. Fifteen feet wide, direction, south; slate alongside much distorted. 
. Fifteen feet wide, direction, south. 
. Six feet wide, direction, south. 
. Eight feet wide, direction, southeast. 
Pwo nw eS 
On Burnt Island, the following were observed :— 
1, Four feet wide, direction south-southeast. 
2. Direction south-by-east. 
3. Direction south-southwest half south. 
4. Direction southwest. 
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