in the Lodes of Dartmoor. 407 



of the veins of micaceous iron-ore at the Hawkmoor and Shapter 

 Mines in the parish of Bovey Tracey, near Lustleigh, and mentioned 

 that one of them contained cassiterite. As these lodes have the same 

 general direction as those at Birch Tor, there can be no reasonable 

 doubt that they are of the same age and differ from them only in the 

 larger proportion of iron-ore they contain. 



From the Hawkmoor and Shapter lodes, which vary in width from 

 2 inches to 2 feet, the amount of shining ore obtained between the 

 years 1892 and 1902 was over 1200 tons (including a small quantity 

 from Plumley and Shuttamoor). The ore was a soft variety of 

 specular iron used almost exclusively as a pigment, and according to 

 official returns realized from £4 to £5 a ton. 



Although I do not contend that all the ferruginous deposits in this 

 district have a similar mode of origin, it is a suggestive fact that the 

 specular-iron-cassiterite veins should happen to occur in a district 

 already so rich in other ores of iron, such as the magnetite and 

 limonite (brown haematite) of Haytor and Ilsington ' and other 

 localities on the west of Dartmoor. 



The nature of the magnetite deposits of Haytor have been studied 

 by (Sir) Clement Le Neve Foster, J. H. Collins, and Dr. Busz, and 

 the results of their work are of interest in this connexion. Dr. Busz 

 examined the ore microscopically, and discovered it to be associated 

 with fibrous hornblende and a little apatite and garnet.- Dr. Foster 

 in 1875 stated that the ore contained, in addition to magnetite, 

 actinolite, garnet, axinite, some iron pyrites, chalcedony, chalybite, 

 and fluorspar. He made alternative suggestions regarding its origin, 

 stating that the ore might be either metamorphosed bedded iron- 

 ores, i.e. contact-altered beds of iron-ore once similar to those of 

 Cleveland, or else the result of deposition of iron-ore along beds by 

 means of ferruginous emanations derived from the granite.' 



After visiting the magnetite mines near Haytor I carefully examined 

 typical specimens of the ore. Although entirely within the meta- 

 morphic aureole of the Dartmoor granite, the general structure of the 

 ore and its relation to the country rock left no doubt in my mind of 

 its being an epigenetic deposit and not the result of contact meta- 

 morphisra acting on a ferruginous bed. Nor are there any greenstones 

 in the mine to account for the presence of the magnetite. The country 

 rock consists of banded Culm sediments, some layers of which show 

 contact alteration phenomena, such as spotting, while others are tough, 

 fine, compact, siliceous bands or coarser micaceous sandy layers, varying 

 from a fraction of an inch in thickness to several inches. Here and 

 there thin veins of granite penetrate the beds. The ore itself consists 

 mainly of hornblende and magnetite, and occurs along certain bands 

 in the sediments. In these orey bands the magnetite occurs as 

 a microscopically fine crystalline layer, ranging up to a foot or so in 

 thickness, which either ends off abruptly against the adjacent siliceous 



1 Over 45,000 tons of iron-ores were raised between 1858 and 1882 from the 

 parish of Ilsington. 



- Neu. Jahrb. f. Min. u. Geol. (Bauer), 1899-1901, vol. xiii, p. 102. 



^ C. Le Neve Foster, " Notes on Haytor Iron Mine " : Quart Journ. Geol. Sec, 

 1875, vol. xxxi, p. 628. 



