648 C. LE NEVE FOSTER ON THE GEE AT FLAT LODE 



near Penstruthal mine south of Redruth . The pseudomorphs are more 

 than an inch long by | inch wide, and are imbedded in a mass of 

 schorl with a little quartz. Killas is also often seen altered into a 

 schorl-rock ; but here the two minerals are disposed in layers ; 

 sometimes it is schistose (tourmaline schist) ; at other times compact 

 (capel). (" On some Tin Lodes in the St. Agnes District," by C. 

 Le Neve Poster, Trans. Roy. Geol. Soc. Cornwall, vol. ix. part. iii. 

 1877.) 



It must not be supposed that schorl-rock is the only form of altered 

 granite. The conversion of granite into "Greisen" is not uncommon ; 

 and Prof, von Cotta* has given ample proof that the fine-grained 

 dark-coloured Zwittergestein has also been derived from the same 

 rock. However, without going out of Cornwall, it is easy to find 

 additional instances of the curious changes which granite may 

 undergo. In the parish of "Wendron particularly there are some re- 

 markable tin-deposits which deserve special mention on this account. 

 I have already described East Wheal Lovellf, and I will now briefly 

 explain the principal features of the deposits at three other mines 

 known as Balmynheer, The Lovell, and South Wendron. 



Balmynheer mine lies about 2| miles N.E. by JS". from Wendron 

 Church, and is remarkable for presenting a large irregular mass of 

 stanniferous rock. The mode of occurrence will be easily understood 

 by reference to the accompanying section (fig. 7) . 



Fig. 7. — Section at Balmynheer. 



S. N. 



.A 



A > A a - ; ; • • • : : 

 «* i A " s ■%'■ 



I * G A V>- 

 * A H +'-*'' 



* * *■ * A » A 



Scale. 990 



sS A * a y -A 



.^^ G 



'. ', ' * « *."* *t*N* 



A ' • ",*..*.•.»" 



. go~ itv =■ J. /oat.. 



* A. * 

 4 A v > , 



. * «B*> • 



GG. 





AA. Slide. 



xoso xo 20 so aii soTcet, 



BB. Stanniferous rock. 



Granite 



GG is ordinary granite. B B is the tin-bearing rock, which occurs in 

 the form of a mass from 30 to 50 feet in thickness, dipping N. at an 

 angle of about 30°, following, in fact, the slide A A. This slide is merely 

 a vein of white clay with a little quartz and mica, and is about 6 

 inches thick. Its course is about E. 32° IS. (true), and the dip N. 

 The tin-rock is a mixture of quartz, chlorite, gilbertite, iron- 



* Festschrift zum hundertjahrigen Jubilaum der konigl. sachs. Bergakade- 

 mie zu Freiberg, p. 156. Dresden : 1866. 



t Trans. Eoy. Geol. Soc. Cornwall, vol. ix. part ii. p. 167. 



