BY LEO A. COTTON. 753 



-systems of Cornwall, by Moissenet*, has proved of much value in 

 the economic working of the mines. 



It is proposed to devote some attention to the fracture-systems 

 of the Elsmore-Tingha area. These may be considered with 

 relation to dykes, faults, ore-filled fractures, and joints. At 

 Elsmore an area about one-quarter of a mile square has been 

 bared by surface-sluicing, and the tin-bearing reefs lie exposed on 

 the surface in a most exceptionally favourable manner for 

 studying their distribution. A series of sections was made in a 

 direction nearly perpendicular to the previously ascertained 

 general bearing of the reefs, and, from the data collected, the 

 accompanying plan (text-fig. 2) has been constructed. The 

 point marked A is 850 yards distant, in a direction S. 4° E., from 

 the south-west corner of Portion 246, Parish of Anderson, County 

 of Gough. The general north-easterly trend of the veins is at 

 at once apparent. 



From the tabulated list given (Table i., p. 757), which includef> 

 all the veins shown on the plan, it may be seen that rather more 

 than 97 per cent, of the reefs lie within that third portion of the 

 possible azimuths lying between N. 5° W., and N. 55° E. This tabu- 

 lated list has been arranged to show the tendency of the reefs to 

 cluster round certain directions. The two most prominent direc- 

 tions are N. 25" E., and N. 39-4° E., the latter being most strongly 

 developed. As will be seen from the plan, these different systems 

 of fracture often intersect. The system bearing 0° has some 

 important fractures, and the systems bearing 16 5°, SI'S", 45^ 

 and 53 2° east of north are all well developed. 



Though many of the reefs intersect, it is quite common for one 

 reef to terminate where it junctions with another. This abrupt 

 termination of one fracture on another is very characteristic of 

 fissures produced by torsion. Daubreef and Beckeri have 



* Moissenet, Prof. L., "Observations on the Rich Parts of the Lodes oT 

 Cornwall." Translated by J. H. Collins, 1877. 



+ Daubree, A., Etudes synthet. de Geologic experimentale, 1879. 



:t Becker, G. F., "The Torsional Theory of Joints." Trans. Am. Inst. 

 Min. Eng. xxiv., 1894. 



