and Volcanic Substances. 215 
of black augit, of Leucite, volcanic hornblende, nepheline, 
Meionite, sommite, Idocrase. Doubts have been entertain- 
ed whether these were pre-existent crystals, or the effect 
and product of igneous fusion, or the effect and product of 
subsequent filtration into the cells, vesicles and cavities of 
the Lava containing them. See Borkowsky on Sodalite. 
Breislak found a chrystal of Augit inside a chrystal of Leu- 
cite. Inst. § 682. 
Beside these chrystals, the following have been found ac- 
companying Lava; Garnet, Hyacinth, Zircon, Sap- 
phire, Spinelle, Peridot, Epidot, titaniferous sidero-calcite, 
Tremolite, Gyps, Hauyene, Zeolyte, Sodalite, Tafelspar, 
Topaz, Humite (Bournon.) In fact, we need not won- 
der at finding the minerals which accompany primi- 
tive rocks, accompanying Lava also ; sometimes chang- 
ed, sometimes unchanged. I Spalan. 78. In the vesi- 
cles or cells of Lava, the minerals commonly found, are 
Leucite (in Italy) Peridot, Zeolyte of various kinds, Preh- 
nite carbonat of lime as at A{tna, at Lipari, 3 Spalan. 228, 
in Iceland. 7%. Ed. Trans. 90. Quartz, Agate, chalcedony, 
green earth. Forming amygdaloids, toadstones and geo- 
des; the crystals in the cells are probably infiltrated. 
Various specimens of these, are in every cabinet of tolera- 
ble extent. The Lavas containing crystals more or less 
perfect, of Felspar, are porphyritic Lavas. Lavas contain- 
ing Zeolite, Prehnite, Agate Chalcedony, mentioned nouv. 
Diet. d’hist. natur. Tome 17, p. 390. Lavas cut through 
all metallic veins, and rarely envelope any metalline sub- 
stance. Galena is said to have been found in whin (Kidd 
102.) but such a case is accidental and rare, though very 
possible. Vegetable and animal remains have been found 
adhering to Lava and enclosed in it. Breisl. § 700. 1 Humb. 
Pers. Narr. 241, see the question discussed in 3 Breisl. p. 
251. Ihave a shell adhering to the slag of an iron furnace. 
Lavas are sometimes very extensive. Dolomique notices 
one of ten leagues. A stream from the north side of Atna, 
according to Recupero, extended forty miles. Lord Win- 
chelsea mentions another in 1669, fifteen miles long by 
seven broad.’ Pennant states the current from Hecla 
in 1784 at ninety-four miles one way and fifteen another, 
and from eighty to one hundred feet thick. The 
currents in the Isle of Bourbon produced thirty million tois- 
