284 ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 



Of the said " contemporaneous veins," probably none are truly 

 contemporaneous. Most of them seem to be segregations into 

 shrinkage cracks of small longitudinal extent and very irregular 

 form, results of chemical reactions in the rocks themselves — or 

 re-arrangement of particulars, &c., &c., while the elvan- courses 

 may be looked upon as injections into fissures, which often 

 exhibit evidence of faulting. 



Adopting the well recognized principle already indicated in 

 Chap. II and Plate X (see Journ. E.I.C., 36, p. 140), that the 

 traversing lode is newer than that traversed, he grouped the 

 lodes, &c., of Cornwall under the following eight categories : — 



1. — The oldest Tin lodes, mostly underlying northwards. 

 2. — More recent Tin lodes, mostly underlying southwards. 

 3. — Oldest East and West Copper lodes, mostly with a 



northerly underlie. 

 4. — Contra Copper lodes. 

 5. — Cross-courses. Bearing generally within 20° of 



North. 

 6. — More recent Copper lodes. 

 7. — Cross-flucans. 

 8. — Slides. 



Actynolite and thallite in slate and greenstone. 

 Axinite in greenstone and slate. 

 Garnet rock in greenstone and slate. 

 Prehnite rock in greenstone and slate. 

 Chlorite in greenstone. 

 Irestone (ferruginous greenstone) in slate. 

 Serpentine in greenstone and serpentine. 

 Greenstone in greenstone. 

 Asbestos in serpentine. 

 Agate in serpentine. 

 Calcite in limestone. 

 Jasper in mineral veins. 

 Opal in mineral veins. 

 Fluor spar in mineral veins. 

 And the following doubtful veins, viz : — 

 Veins of granite in slate. 



,, steatite in serpentine. 



,, calcareous spar in serpentine and in slate. 

 Elvan courses. 

 Certain veins of oxide of tin in granite. 



