A. A. Julien on Sponge-Spicules. 379 
; b, Si aypegastae > stellated groups. Color white. Opaque. 
ri 
No analysis has been made of the material but I suppose it to 
be identical with that of the original crystals, minus the water. 
ey occur intermixed with the original crystals; and also as 
solitary white groups, dotting over in ) marked contrast the dark 
brown phosphatic lining of cavities in the limestone. 
In conclusion it may be observed that specimens o o these 
phosphatic minerals are exceedingly ra ew having been 
found since my departure from pia sabe Gn the spring of 1864). 
Good specimens of the pseudomor are also uncommon, 
though imperfect or drusy crystals have oecanicnale been found 
in tolerable abundance on the opening of some new vein. It is 
a universal rule, when the original or the pseudomorphous crys- 
tals oceur in cavities of the limestone, that they are never in 
direct contact with the matrix, a film or thin layer of a common 
brownish material, rich in bone- phenpaate of lime, always inter- 
vening. As to my theory in regard to the origin and history of 
these minerals and of their pseudomorphs, I must refer to the 
coming publication of my general observations on Sombrero 
lt is sufficient here to state that they have undoubtedly been 
. pecsied from the salts of the superficial guano-deposit brought 
down in solution by carbonated rain-waters into the joints of 
the limestone. 
: School of Mines, Columbia College, New York. June, 1865. 
a Art. XXXIX.—On Two Varieties of Sponge-Spicules ;* by 
ALExis A, JULIEN. 
In clearing the white coral-sand out of a crevice of the rock 
near the east cliff of the Key of Sombrero, W. I., a loose mass of 
i snow-white acicular fibres was found, associated with fragments 
Of coral, shells, etc., at the height of thirty- six feet above the sea, 
and imbedded in the sand at a depth of about three feet from 
the surface. Among these fibers the two following varieties 
aS hat distinguished, ‘the former composing the bulk of. 
re “Acicular, tubular, and gently-eurving spicules (fig. 1, a), 
tapering from the middle toward each end, at first very gradu- 
ally, and then rather suddenly at a short distance from: ¢ _ 
toa rounded point. 
My grateful acknowledgements are due to Prof. O. N. Rood of the School of 
“Mic Columbia C, for the use of his microscope and for general 
aad galvicn, toto eb OF Chandler of the School of Mines, for the facilities of 
laboratory.—a. A : 
