66 NEW YORK STATE MUSEUM 



does not wish to discuss at length the points for and against each 

 of these views in this place, reserving it for the fuller space which 

 will be afforded by a separate bulletin on the Port Henry and 

 Elizabethtown quadrangles, now in preparation. If supporters 

 of the sedimentary view will add to the rock names used above the 

 word gneiss, or change the rock names into the form of adjectives, 

 so as to have syenitic gneiss, gabbroic gneiss, dioritic gneiss, etc., 

 thus using them as short cuts of expression for the mineralogy of 

 the gneisses, they may still be regarded from the point of view of 

 sediments. The full discussion requires chemical analyses, and 

 more ample illustration. Whether we have, however, parallel 

 metamorphosed sediments, or differentiated layers of eruptive 

 rock, the structural features of folds and horizons are not changed 

 and for practical purposes these are the really important considera- 

 tions. The ores, which occur at Mineville as integral members of 

 the syenitic series, are in the form of layers conformable to such 

 banding or foliation as appears in the rocks. These layers bulge 

 and pinch to a remarkable degree, and in the case of the Old Bed 

 group (or Mineville group of the writer's earlier paper) extend in a 

 practically unbroken stretch for half a mile exhibiting at the same 

 time a very complex and puzzling fold ; while in the Barton Hill 

 group the extent is still longer but the structure is simpler. The so 

 called Cheever bed with its extensions must be fully half a mile in 

 length, but all the others are smaller. The bulges and pinches give 

 a marked podlike or lenticular form so that at Mineville the ore 

 bodies are a series of richer and thicker shoots whose long axes 

 run in a parallel northeast and southwest direction. 



The ores are granular masses of magnetite which in the Barton 

 Hill group were prevailingly of Bessemer grade, but which in the 

 Old Bed series are high in phosphorus from disseminated apatite. 

 These are now run through a magnetic mill and freed of the apatite 

 to such a degree that they are a better grade for the furnace and the 

 apatite is salable for fertilizers. Occasionally where the apatite 

 is relatively abundant and the ore occurs near a fault or line of 

 crushing which has caused decomposition of the augite both in the 

 ore and in the country rock, red hematite has been yielded and has 

 filtered into all the little crevices and has given the ore a red color. 

 This variety is the so called "red ore" of the cross-section. In 

 the same way the country rock is also colored red. 



In thin section the rich Old Bed ore reveals a noticeable amount 

 of the green augite, characteristic of the syenitic wall rock. This 

 mineral has certain optical properties that suggest a variety rich in 



