RED COLOR OF CAMBRIAN AND CARBONIFEROUS. 63 



proportion of this material ranges from about one-half of one per cent to 

 as much as five per cent by weight of the mass. As further oxidation of 

 these crystals of magnetic iron goes on but slowly, the deposits in which 

 they finally come to rest may contain a large share of the material which is 

 to be, by further change, dissolved and distributed through the bed. Even 

 where the ferruginous matter has been accumulated between the fragments 

 of rock in the form of a thin vein or coating separating the bits, it may by 

 a further process of change lose the iron in a greater or less measure and 

 become a mere stain. 



