MAGNETIC OXIDE OF IRON. 91 



two plans, one of which is on a large scale, to show the thin vein of iron which projects from 

 one of the large masses into the rock ; the other exhibits a plan of all the important masses 

 which have been examined in this immediate vicinity. There is no attempt to exhibit the real 

 shape or form of the masses ; this forms, however, a remarkable contrast with the views of 

 the same mineral in Peru, and in many of the adjacent towns where gneiss is the predominant 

 rock. (See Plates III. and IV.) 



Veins, their Structure, etc. 



In their form, ihey are unquestionably lodes or genuine veins, sometimes of considerable 

 longitudinal extent, and often coinciding nearly in direction with the strata. They are be- 

 tween walls of gneiss or granite, varying in width from one to thirty or forty feet. The rock, 

 however, is rather a granitoid gneiss in many places ; in others it is hornblende, the belt of 

 country being underlaid principally by a rock which in the main is stratified, but its charac- 

 ter in this respect is not well marked. The more perfect the stratification, the more distinct 

 are the veins. 



An important feature presents itself in regard to the distribution of the magnetic oxide 

 through the northern counties : it is its occurrence in parallel belts, for rarely do we find a 

 single insulated vein or mass. This feature is one which is favorable to the manufacture of 

 iron ; increasing the quantity of ore, and furnishing it of different qualities, some of which are 

 adapted to the manufacture of bar, and others, to that of pig iron and other castings. 



I remarked above, that the direction of the vein often coincides nearly with that of the 

 strata ; this applies to the dip as well as to the strike. For limited distances, the coincidence 

 is often perfect, still, in most cases there is a deviation ; the vein, as it comes up from below, 

 passes through the strata, and not between them ; and as it is traced longitudinally, it will be 

 found to cross them in its onward course. The common strike of the veins is north-northeast 

 and south-southwest, yet it is not constant. The amount of dip varies from thirty to seventy- 

 five or eighty degrees. 



The veins of magnetic oxide may be described comprehensively, as consisting of ore and 

 other minerals, particularly limestone, hornblende, feldspar and quartz, all of which are 

 arranged longitudinally, somewhat in parallel stripes, the ore frequently forming the smallest 

 part of the vein. Its usual arrangement is in rather ovoid masses, disposed with the longer 

 axis in the direction of the course of the vein. Sometimes they are numerous and small, 

 being strung together, and touching each other at their points ; in others, those masses are 

 large, extending many feet, the same arrangement being preserved, and each ovoid mass of 

 ore being separated from others by a thin partition of the gangue. But there arc instances 

 where the vein seems to be composed mostly of ore ; and others in which the foreign minerals 

 are about equally diffused in the vein. Where such a structure and arrangement prevails, 

 the foreign mineral is mostly quartz, and the ore in the rock presents a mixture of black and 

 grey, the latter being sprinkled over or through the dark ground of ore. 



Another feature worthy of notice, is the liability of the vein to be shifted or moved to one 



