144 Prof. Chapman's Miner alogical Notes. 



(9.) Detection of Manganese in Limestone Rocks. — A consi- 

 derable number of limestone rocks contain a minute proportion 

 of carbonate of manganese. I have noticed this more particularly 

 in the darker magnesian limestones of the Permian epoch, but 

 also in various other limestones of different ages and from differ- 

 ent localities. The common blowpipe-test — fusion with carbonate 

 of soda — generally of so delicate an appreciation, here fails, even 

 on the addition of nitre, to point out the presence of manganese. 

 This is owing to the insolubility of the limestone in the carbo- 

 nate of soda. If, however, a very small quantity of borax be 

 added, so as to attack and dissolve a portion of the mass, the 

 well-known greenish-blue enamel is quickly produced. 



(10.) Barytine. — The crystals of barytine (BaO, SO 3 ) from 

 the fuller's-earth pits in the greensand formation of Nutheld, 

 near Bletchingly in Surrey, possess the general configuration of 

 the Cumberland, Schemnitz, and other crystals in which the 

 basal form P (OP of Naumann) predominates. The forms usually 

 present in the Nuffield crystals are the prismatic forms P and 1), 

 and the diaxial pyramidal forms |A, \K, and E. L, A, and AA 

 are occasionally seen, as also the triaxial forms 0, ^0 ; but the 

 latter are in general very minute. 



In Naumann's notation, P = OP, L=ooPoo, D=ooP, 



A=Poo,E=Poo, = P. 



D:D = 101°42'; P:A = 121°46'; P : 4A = 141° 4' 30" ; 



P:iA=158°0'30"; P:AA = 162°6'; P:E127°15'; 



P: = 115° 39'. Axes: V = 1315; T=l; F = 08141. 



Viewed in regard to their general configuration, the crystals 

 of sulphate of baryta fall into six groups. In the following 

 tabular arrangement, the vertical axis is denoted by V, the frontal 

 by F, and the transverse (right and left axis) by T. 



Group 1, with P predominating. — The crystals of this group 

 have a more or less flattened or tabular appearance. Localities : 

 Felsobanya, Schemnitz, Freiberg, Cumberland, Nutfield, &c. 



Group 2, with AA predominating. — Crystals elongated parallel 

 to axis T. Puy-de-dome,Marienberg, Przibram, &c. A combi- 

 nation frequently met with in trap and volcanic districts. 



Group 3, with E predominating. — Crystals elongated parallel 

 to axis F. Puy-de-dome, &e. This configuration is very rare. 



Group 4, with P and E predominating conjointly. — These 

 crystals are also elongated in general along the frontal axis, and 

 are much more common than the above. Mies in Bohemia, Frei- 

 berg, Baden, Lancashire, Nutfield, Cheshire in Connecticut, &c. 



Group 5, with iA and E predominating.— These forms pro- 

 duce an irregular octahedron, generally elongated along the 

 axis F. Puy-de-dome, &c. 



