THE 



PHILOSOPHICAL MAGAZINE 



AND 



ANNALS OF PHILOSOPHY. 



[NEW SERIES.] 



APRIL 1829. 



XXXVII. On the Junction of the Granite and the Killas Rocks 

 in Cornwall. By Messrs. Von Oeynhausen and Von 

 Dechen. 



[With a Plate.] 

 [Concluded from p. 170.] 



VIII. Car daze Tin Mine near St. Austle. 



/^ARCLAZE tin mine is situated about two miles on the 

 ^^ north of St. Austle, in the granite, and very near to the 

 junction of this rock and the killas (figs. 21 & 22). The 

 junction is nearly perpendicular, but dipping to the south; the 

 killas is decomposed into an earthy and argillaceous mass ; but 

 the stratification is nevertheless distinct, the strata underlie 

 rapidly to the south; therefore the killas is in a position uncon- 

 formable to the granite. The mine forms a large excavation, 

 open to the day, and is said to be 250 fathoms in length, one 

 hundred fathoms in breadth, and twenty-one or twenty-two fa- 

 thoms in depth. The direction of the greatest length of this 

 remarkable opening is 30 degrees north of west. In the eastern 

 ])art of the excavation are several shafts sunk below the bottom 

 of it, by which tin ore is raised to the depth of ten fathoms 

 under the adit. The granite is here of a light yellowish white 

 colour, and extremely decomposed ; the felspar is changed 

 into a white China-clay, and shows the contours of crystals 

 of the common size ; schorl occurs very frequently here. 

 This granite differs from that kind which commonly prevails; 

 the twin crystals do not occur in it; but it is very nearly 

 the same as at Cligga Point. The common kind of granite is 

 found of great extent in the neighbourhood, and used as build- 

 ing stone under the denomination of Moorstone. 



The granite at Carclaze is intersected by numberless veins 

 N.S. Vol. .•;. No. 28. April 1829. 2 I and 



