ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 291 



" great cross-course " near Treskerby Mine at an acute angle 

 and heaves it considerably to the right. It also heaves the 

 junction of granite and slate in the same direction. Delabeche 

 speaks of the great cross-course as heaving the granite junction, 

 but a close examination of the district shews that the great 

 cross-course is also itself heaved at this point. The heaves by 

 this cross-course are similar in direction to those by the great 

 cross-conrse, but generally much less extensive. Several other 

 cross-courses in the Redruth, Illogan, and Camborne district 

 appear to belong to this period, among them probably one or 

 more of those which traverse the United Mines and possibly 

 that which divides Dolcoath Mine from Cook's Kitchen. 



7. — The so-called " trawns " of the St. Ives and Lelant 

 district are probably some of this age and some older. None of 

 them contain either tin or copper ores (except perhaps close to 

 their intersections of such lodes). Occasionally there is a little 

 iron ore present, but usually they contain granitic matter only 

 while passing through granite, and slaty matter where they pass 

 through slate. 



8. — A great many of the " guides " of the St. Just district 

 belong to this period, others appear to be older. 



Class XII. — Newest East and West Tin and Copper Lodes. 



These are probably very numerous, but they seem to occur 

 chiefly in the mining districts from St. Agnes to Gwinear, the 

 ''West Central District" of Mr. Robert Hunt. Up to the 

 present we have perhaps no absolute proof that some of these 

 are earlier in origin than the cross-courses and flucans of Grroup 

 XIII, but their earlier type of filling would seem to indicate 

 that such is the case; and at Penhalls mine the E.W. tin- 

 bearing slides are certainly older than the Penhalls cross-course. 

 The following lodes also belong to this class, in all prob- 

 ability, viz. — 



Wheal Duffield, Holman's lode. 



Relistian lode. 



Trevascus lode. 



Dolcoath, North Entral lode. 

 South ,, 



