408 



D. A. MacAUster — Camterite and S2)ecnlar Iron 



bands or merges insensibly on both sides into a mass of radiating, 

 curved, green fibres and sheaves of hornblende, which in turn ends 

 abruptly against the adjacent beds of the Culm. Throughout the horn- 

 blende small, well-formed, or microscopically fine crystals of magnetite 

 may be seen. The magnetite also occurs as well -formed octahedra 

 encrusting cracks in the hornblende mass and sometimes in association 

 with transparent vein-quartz and a micaceous mineral. As a whole 

 the structures are reminiscent of those seen in some tin veins in 

 killas, in which tin -ore occupies the same relative position with 

 regard to greisen, chlorite, or schorl-rock that the magnetite does to 

 the hornblende (Fig. 4). 



Sh. 



Sh. 



M. M. T. 



////////'///////"/' 



Gr. 



Sh 



Fig. 4. Diagram illusbating the structure of the magnetic iron -ore deposits at Haytor 

 (reduced to f nat. size). M., dense, finely crystalline magnetite with cracks encrusted 

 with well-formed crystals; a little fibrous hornblende is seen in places; T., transition 

 between magnetite and hornblende ; S., fibrous hornblende with scattered crystals and 

 specks of magnetite ; Q., dense fine siliceous rock resembling a very fine quartzite or 

 chert; (SA., spotted shale ; Gr., granite vein. 



It appears to me that it is possible to link the ore genetically with 

 the tin-specular-iron veins of Birch Tor, on the assumption that they 

 were impregnations or metasomatic replacements along calcareous beds 

 of the Culm at the time they were undergoing thermal metamorphism. 

 The magnetite deposits may be paralleled with those of Pennsylvania, 

 where calcareous rocks have been replaced by this ore by heated 

 ferruginous solutions.' . It should be borne in mind, however, that 

 there are many lodes of iron in the west of England, particularly 

 those characterized by the presence of chalybite and small amounts of 

 manganese (e.g. Perran Iron Lode, Newquay, and the lodes of 



1 C. Spencer, Bull. 359, U.S.A., 1908. 



