sasde J 
XLVI. Note on some Prismatic Forms of Calcite from Luganure, 
County of Wicklow. By Wiii1aM K. Sorrrvan*. 
* the first edition of his Traité de Minéralogie (Paris, 1801), 
Haiiy distimguished three kinds of prismatic carbonate of 
lime :—1. Chauzx carbonatée prismée, already described by Romé 
de Lisle, and which Haiiy supposes to be derived, in his mole- 
cular theory of decrements by the law d!. According to this, it 
would be the prism produced by modifying planes placed upon 
the lateral edges of the primitive rhombohedron. The second 
he calls chaux carbonatée imitative, and considers to be the prism 
obtained according to the law e? by planes on the lateral angles 
of the primitive. The third, which had also been before de- 
scribed by De Lisle, he named chaux carbonatée prismatique, 
and considered to be also derived according to the law e?. He 
mentions four varieties of this form: a, alternating—having 
three alternate wide faces and three intermediate narrow ones ; 
6, compressed—with two opposite faces larger than the other 
four; c, widened—with four faces wider than the remaining 
two; and d, lamelliform—in very short (7. e. in tabular) prisms. 
Of the crystals of this form he says, “In certain crystals the 
extremities are of a dull white, while the intermediate part is 
transparent. In others the opake part is situated towards the 
axis and surrounded by a transparent envelope. The bases of 
a few exhibited concentric hexagons, and one could even ob- 
serve the extremity of a small internal prism, rising above the 
whole prism.” 
The forms he calls imitative and prismatic being obtained by 
the law e?, contain the same prism; the prismatic faces which 
have been observed among the varieties of calcite belong, 
therefore, to one or other of those prisms. Dufrénoy, who uses 
the nomenclature of Haiiy, as modified by Levy and himself, 
represents the faces of the first prism, or that on the edges of 
the rhombohedron, by the symbol d' (u of Haiiy), and the pris- 
matic, or that on the angles, by e* (c of Haiiy). Of course each 
of these prisms is completed by the modification a! on the 
summit angle, which produces the horizontal plane forming the 
base. 
According to the German crystallographic methods, prisms are 
looked upon as mere limiting’forms. Mohs and Haidinger con- 
sider d’ to be the limiting form of the pyramids, the former 
expressing it by the symbol P + and the latter by o P, which 
is the one adopted by Zippe in his summary of all the observed 
forms of carbonate of lime +. The second prism, e*, is considered 
* From the Atlantis, No. V. p. 176. Communicated by the Author. 
+ Uebersicht der Krystallgestalten des rhomboedrischen Kalk-Haloids, 
