J. D. Dana’s Mineralogical Contributions. 251 
parallel to which composition takes place, must be the true rep- 
resentative of the fundamental prism of Aragonite and the allied 
carbonates. 
The relations of the sulphates and carbonates have been shown 
on page 53 of this volume, and had previously been brought out 
by Hausmann. It is there seen that the unit prism and domes 
of the sulphates and carbonates are as follows. 
Barytes, a sulphate, (12) 116° 20’ (Z)78° 20° (1%) 105° 24/ 
Anhydrite,  “ “ 118° 35! oT ae pee Side 24 
Aragonite, a carbonate, (Z) 116° 10’ = (17) 81° 40’ (17) 108° 26’ 
_ Adopting the prism of 119° 40’ in Leadhillite, as correspond- 
ing to the prism of 116° 10’ in Aragonite, as above shown, the 
corresponding angles are for 
Leadhillite, . . . 119° 40/ 16° 44! 107° 26’ 
For Barytes and Anhydrite (sulphates) the prisms of 78° 20’, 
77° 4’ (the supplements of which angles are 101° 40’ and 102° 56’) 
are ordinarily taken as the vertical prisms; while in Aragonite, 
that of 116° 10’ is the vertical prism; the difference being one of 
Position. The question now is, therefore, whether the prism of 
119° 40 is the true vertical prism of Leadhillite, and it is thence 
most closely related to the carbonates, or whether the vertical 
prism is that of 76° 44’ and 103° 16’, making its closest relation 
to the sulphates. The latter is the view adopted by the author 
in a former paper and in the lettering of the above figures, and 
it appears to be sustained by the following reasons, 
1. The planes of the prism of 119° 40’ have not yet been ob- 
served, or if observed they are of very rare occurrence. In fig- 
ure 1, the occurring planes are 12 and 4%, without 17; and in the 
other zones, we find 1, 2, 4, without the plane 1. Or, putting 
Sut by the author in the last volume of this Journal, page 
favor the view that the prism of 103° 16’ is the true vertical 
Ptism. As this point is important, the facts are here repeated. 
Rhombohedral. Trimetric, ‘onoclinic (basal cleavage.) 
Calcite (Ca 6) 105° 5’ Aragonite, (a 6, 116° 10’ Barytocalcite (Ca, Ba)C, 95° 8’ 
Dreelj : Anglesite Pb§, 103° 38’ ~ yt 
990.5 (Os, Ba)5; Anbydtite Ga S, 102° 56’ } Glauberite (Ca, Na)S; 83° 
Barytes Ba §, 101° 40/ 
“No ® PbS+3Pb G { Leadhillite, PbS+3Pb C { Lanarkite, PbS-+Pb , 85° 48" 
estos? 10) 
