Art. XL] Watson, The Leopa7'ditc of North Carolina. 



229 



superficial phenomenon, and perhaps does not extend to any 

 very great depth. 



CHEMICAL COMPOSITION. 



The chemical composition of the rock is given in analysis 

 I of the table of analyses. The analysis of leopardite was made 

 by Dr. F". A. Genth from the freshest fragments of the ground- 

 mass obtainable. The most striking features of the analysis are 

 (i) the very acid character of the rock, manifested in the high 

 SiO« content ; (2) the nearly complete absence of CaO and 

 MgO; and (3) the increased Na^O which is in excess of the KjO. 

 The analysis, however, harmonizes closely with the microscopic 

 study of thin sections of the rock, for the absence of ferromag- 

 nesian minerals accounts for the very slight amount of MgO 

 present, while the practical absence of CaO and the large per- 

 centage of NaiO prove the plagioclase to be albite, as indicated 

 above by the microscope. 



TABLE OF ANALYSES. 



SiOj 



Al,03 



FeA 



FeO 



MgO 



CaO 



Na^O 



K.p 



HjO-iio°C._ 

 np-f no°C. 



TiO^ 



I'A 



ZrOj 



MnO 



SrO 



BaO 



Lip 



NiO 



CO, 



TotaL 



75-9-' 

 M-47 



0.09 

 0.02 

 4.98 

 4.01 



0.64 



II 



79-75 



10.47 



0.64 



0.92 



0.13 



0.15 



1.36 



6.01 



0.08 



0.60 



0.15 



trace 



0.05 



trace 



trace 



0.06 



trace 



100.37 



III 



79.57 

 1 1. 41 

 0.20 

 0.70 

 I little 

 0.21 

 3-46 

 3-52 

 0.18 

 0.61 



O.I I 



trace 



0.05 



IV 



7312 

 14.27 

 0.51 

 0.26 

 0.24 

 1. 10 



3-43 

 4.90 

 o.b8 



0.73 

 0.08 

 0.03 



0.06 

 trace 

 trace 

 trace 



0.77 



ioo.i8 



72.85 

 13.78 

 1.87 

 0.36 

 0.42 

 0.87 

 4.14 

 4.49 

 0.22 



0.54 

 0.44 



0.06 



99.87 



11. 



Quartz porphyry (leopardite), one and a half miles east of Charlotte, 

 Mecklenburg county, North Carolina. American fourtial of Science, 

 Vol. XXXIII (1862, 2d ser.), p. 198. F. A. Genth, analyst. 

 Quartz porphyry — two and a half miles northwest of Blowing Rock, 

 Watauga county. North Carolina. Petrographic data by Arthur 



