490 RECORDS. 



it would cool first. Convection currents would tend to bring 

 new supplies of material to the outer zone where the chromic 

 oxide would be deposited as chromite. 



This theory would account for all the vagaries of chromite 

 deposits, their pockety nature ; the shooting off of apophyses 

 from the main masses of the chromite into the peridotite, the 

 widening and pinching of the chromite lodes ; and the appar- 

 ently non relation or connection of one pocket of chromite with 

 another. The masses of chromite that are found in the midst 

 of a peridotite formation, which at the present time are isolated 

 and have no connection with each other, were at the time of 

 their formation part of the chromite concentrated near the bor- 

 der of the peridotite. 



In mining for either chromite or corundum it is in that deposit 

 found near the contact of the peridotite with the gneiss that a 

 large deposit of either of these minerals would be expected to 

 be found. 



Chemical Composition. —Yrova an examination of the analysis 

 of chromite it is shown that a nearly pure chromite, with the 

 composition FeOAO, is rarely found in nature. With the ex- 

 ception of three, in all the chromite analyses examined, alumina 

 and magnesia were invariably present, and this would seem to 

 indicate that the molecule of the mineral now called chromite is 

 not pure FeOAO, but is a combination of the three isomorphous 

 molecules; FeOA203 ; MgOAp3 ; and MgOAl,03. The 

 ratio of the FeOAp3 to the MgOA203 or MgOAl,03 is gen- 

 erally 8 to lo : I. 



An analysis of a chromite from Webster, Jackson Co., N. 

 C, gave as A2O3 — 95^0 ; AI2O3 — 29.28^0 ; FeO — 13.90, and 

 MgO — 17.31. This gave for the formula of the chromite, 

 ratio of the molecule MgOA.,03 observed in any of the chromite 

 examined. 



It was noticed that the magnesia usually varied with the 

 alumina, those rich in alumina being correspondingly rich in 

 magnesia. 



The second paper was by Professor D. S. Martin, entitled 

 Notes from the Semi-Centennial Meeting of A. A. A. S. 



