140 Journal of the Mitchell Society [March 



ably dolomite, a few plates of phlogopite and large irregular masses 

 of magnetite. The mica is in streaks of plates extending in nearly 

 straight lines through the section with the individual plates lying be- 

 tween adjoining carbonate grains and more frequently than otherwise 

 near the magnetite. This mineral is often in large areas with very 

 ragged boundaries, the salients of which project considerable distances 

 between the grains of carbonate, or between contiguous twinning 

 lamellae. Occasionally^ a smaller grain appears to be enclosed in grains 

 of what is regarded as dolomite, and in other instances the larger 

 masses appear to enclose small grains of the carbonate. From the fact 

 that the carbonate inclusions polarize uniformly with the large car-, 

 bonate grains surrounding the magnetite it is thought that the ap- 

 parent inclusions are merely portions of projections that extend into 

 the embayments of the magnetite and that their appearance as inclu- 

 sions surrounded by magnetite is due to the fact that the section was 

 cut through the boundary between magnetite and carbonate. 



The richer ore differs from the poorer ore mainly in the larger 

 sizes of the distributed magnetite grains and especially in the much 

 greater sizes of the magnetite lenses. Some of the latter are a foot 

 or more in length and five or six inches in diameter. A photograph 

 showing the contact of one of the lenses with the surrounding marble 

 is reproduced in pi. 26. 



The greater portion of the ore, as has been related, is mainly a 

 coarsely crystalline marble containing grains and lenses of magnetite. 

 In many places, however, it contains dike-like masses of a bright 

 green color, which proves to be a fine-grained aggregate, mainly of 

 granular actinolite which, where shearing occurs, is changed to a mass 

 of fibres of bright green actinolite. Often magnetite is present in the 

 granular aggregate, and this is noticeably more abundant near the 

 contact of the green layer with the marble. Indeed it not infrequently 

 happens that there are distinct lenses of magnetite at the contacts of 

 the two rocks even though magnetite may not be present elsewhere 

 in association with the green rock, and occasionally a continuous thin 

 layer of magnetite separates the two for considerable distances. The 

 actinolite layer passes into the carbonate rock by a very gradual tran- 

 sition — the, actinolite becoming less and less abundant until it forms 

 a very small portion of the mass. 



In this section the actinolite mass is discovered in reality to be 

 complex. It consists of an aggregate of thin layers and fiat lenses 



