264 FRANK D. ADAMS 



minerals, cementing them together, or as inclusions in the feld- 

 spars. 



Apatite. — The abundance of apatite is a distinct feature in 

 this, as in similar rocks occurring elsewhere. It is always 

 present and was the first constituent to crystallize out, being 

 found in the form of perfect hexagonal prisms with double 

 pyramidal terminations imbedded in the iron ore. It also occurs 

 in the sphene as well as in the iron-magnesia constituents, in the 

 nepheline, and also, although much less frequently, in the feld- 

 spar. Its large amount is shown by the high percentage of 

 phosphoric acid in the analysis of the rock, 1.23 per cent. 

 Another specimen of the rock in which the phosphoric acid was 

 determined by Dr. B. J. Harrington gave i.oi per cent. These 

 figures represent 2.79 per cent, and 2.35 per cent, of apatite, 

 respectively. It is usually somewhat turbid from the presence 

 of minute dust-like inclusions. 



Magnetite occurs chiefly inclosed in the iron-magnesia con- 

 stituents, but is occasionally found in the feldspar. It is black, 

 opaque, and highly magnetic, and is usually allotriomorphic, but 

 occasionally presents an approximation to definite crystalline 

 outline. As shown by the calculation of the analysis of the 

 rock, this iron ore contains a considerable percentage of titanic 

 acid. 



Spliene is not found in more than one-half of the specimens 

 examined. When present it is not very abundant and usually 

 occurs as well-defined wedge-shaped crystals, often of con- 

 siderable size. 



In the accompanying table analyses are given of the normal 

 essexite which forms the greater .part of Mount Johnson, and 

 of the finer-grained olivine-bearing variety of the same rock 

 found at the summit of the mountain. For purposes of com- 

 parison there is presented in the same table the analysis of the 

 essexite from Shefford mo.untain, which belongs to the same 

 Monteregian province, together with analyses of the original 

 essexite from Salem, Mass., and of allied rocks from two other 

 localities. A partial analysis of the transitional rock between 

 the essexite and the pulaskite of Mount Johnson is also given. 



