1917.] Limburgite in British Baluchistan. 297 



first of all pointed out clearly the occurrence of lath-shaped 

 crystals of felspars in the groundmas* of the rock, and accord- 

 ingly the original definition of the rock cannot be accepted 

 now. 1 Specimens from Limbourg hill were examined, fels- 

 par was found in the groundmass and ' felspar is abundant in 

 much of the rock at both ends of the hill, of which the original 

 limburgite, with the base of brown glass, is only a local condi- 

 tion." 2 Among the limburgites that have been described as 

 vet, those from Kathiawar by Mr. Adye,** from the Macedon area 

 by Dr. Skeats and Mr. Summers,* from Balwyn (near Doncaster) 

 by Messrs. Chapman and Thiele, 6 from Southern India by Sir 

 Thomas Holland, 6 from a few places in Bohemia by Hinter- 

 lechner, 7 from the Black Mountain by Soellner," from Sao 

 Thome and Fernando Po by Boese," all show microlites of 

 felspar in the groundmass. While describing the geology of 

 Costa Rica, Mr. Romanes has mentioned the occurrence of a 

 limburgite ' entirely free from felspar,' but at the same time it 

 has been observed that the groundmass has undergone very 

 considerable alteration and become completely devitrified. Dr. 

 Bonney, on a careful examination of this rock ; has shown the 

 great ' resemblance which the groundmass bears to the mineral 

 pseudophite described by both Dr. Teall and the late J. D. Dana 

 as forming a special alteration product of felspar. The resi- 

 dual glass had, therefore, probably the composition of felspar 

 or may even have largely consisted of minute felspar-crystals.' ,0 

 It must also be stated, however, that from several localities 



copische Physiographie der Massigen Gesteine' (1908) Rosenbusch seemed 

 to have changed his original definition, as we find ' die Limburgito und 

 Augitite sind gemoinschaftlich dadurch charakterisiert, dass sie weder 

 Feldspat noch ein feldspathahnliches Mineral als wesentlichen Gemengteil 

 enthalten' (p. 1463). 



1 Geol. Mag. Dec. IV., Vol. VIII, pp. 411-417, 1901. 



» Ibid., p. 416. 



3 Economic Geology of Navanagar State, pp. 93, 95, 97. 



4 Among the seven, types of limburgite described from this area Jour 

 contain felspars in the groundmass. (Bull. Geol. Surv. Victoria, No. 24, 

 P- 27, 1912). * 



J Proc, Roy. Soc. Vict.. N.S. XXIV, p. 126, 1912. 

 ■ Rec. Geol. Surv. Ind., Vol. XXX, p. 19 footnote 

 ] Jahrb. K.K. Geol. Reichnst, Vol. L, 1900, pp. 504. 51*- 

 J Jahrb. K.K. Preuss.. Geol Landsanst., Bd.. XXII, p. 56 j J04. 

 ,. 8 According to Boese in the groundmass of the Sao Tho'nA l.m bur 



g*e ' Feld Spat kommt ilusserst selten vor, seine Menge b / ril ^?f ^^ 

 emrnai 10/ > While describi the Hmburgites from Fernando , Po the 



«w»e author has observed that < ,n der Abteilung de \ ^^l^die 

 H^st einige Gesteine als UmburgUische Basalte boschneben warden ^dw 

 Jachen den Basaltcn und Limburgiten stehen wed sie «**«*»" J 

 gennger Menge fiihren " (N. Jahrb. f. Min Geol. u. Pal J *£&*%£. 

 }* XiV > PP. 275, 307, 1912). Terms like Limburgbasa t, L.mburg-tacny 



" Q e j a G°S 8U f e , St6 T d ^T° f • B Tll30° P l^' ' While describing the 

 limk ^i'. -**•&•* vol. LXVIII, pp. 129-loU, hm* , around- 



^W gl te of the Cripple Creek district, Mr. Stevens says that * hejjj«w 

 ***>* « composed of fine augite crystals, set in a clear, colourless, isotrop 



