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mass the crystals of black oxide of iron have assumed most 
beautiful forms, strikingly like some ferns or minute fir trees, 
and deposited on these are small crystals of a nearly colour- 
less mineral, inclosed in a glassy basis, which is the un- 
crystallized residue. The structure of different portions of 
a mass of 23 cwts. fused and slowly cooled differ very 
materially. Some parts consist of a black glass containing 
irregular, spherical, radiate groups of crystals, varying in size 
up to a diameter of about half an inch. These are so opaque 
that their internal structure cannot be well seen, but on the 
surface, penetrating into the surrounding glass, are many 
objects of a most curious character, far more like organic 
bodies than the crystals we are accustomed to see in rocks. 
Some are extremely like the antennae of insects, rising from 
bases which have curious curved outlines, and from the 
extremity of which they protrude like the plumose tentacles 
of some organic bodies. There are also many hair-like 
groups, twisted into such forms that any one who did not 
know how they had been formed would certainly conclude 
that they were of organic origin. In another portion of the 
same mass some parts are glassy and some stony. In the 
glassy parts are beautiful groups of crystals of black oxide cf 
iron, often in the form of most elegant and highly ornamented 
crosses. The stony part also contains them, and they were 
formed before the crystals whose development caused the 
whole mass to have a stony character. The structure of the 
line of junction of the glassy and stony parts is very instruc- 
tive, and shows the manner in which first one and then 
another kind of crystals was produced. In the more stony 
portion, at some distance from the glassy, the crystals of 
black oxide of iron were not invariably generated before all 
others, but colourless prisms or plates of another mineral 
were first formed, and afterwards the two were developed 
contemporaneously. I have carefully studied similar crystals 
