130 NEW YORK STATE MUSEUM 



as different in origin from the other. The syenite has practically 

 convinced the writer that being igneous itself, it carries inevitably 

 into the same great group of rocks all the associated rocks, whether 

 they consist of acidic, or basic silicates or even of ore itself. Hence 

 this consideration is esteemed of greater weight than the coin- 

 cidence of the pod or lenselike shape with undoubted sedimentary 

 structure, and, in the interpretation of the nature of the ore bodies, 

 the preference is given to igneous processes. 



If we grant for the moment that the ores are of igneous origin 

 and endeavor to understand the possible causes which have led 

 them as well as the more basic and the more acidic phases of the 

 syenitic rocks to form, we find ourselves confronted by great ob- 

 scurity. It is believed by many that some sort of segregative 

 process leads to this separation, just as pots of nickle-copper matte 

 rearrange their composition in a fairly constant way in the few 

 moments of cooling; or as pigs of base bulHon, homogeneous when 

 molten^ are diverse when chilled. Some kind of physical-chemical 

 force must assert itself and produce the variation. In connection 

 with igneous iron ores, whose common mineral magnetite and its 

 associated apatite are the first components of a fused magma to 

 crystallize, many have thought that these two, being heavier than 

 the magma, have settled out by gravity and have become concen- 

 trated as soon as developed. Subsequent flowage might then drag 

 them out into bands, and rearrange their position with regard to 

 relative depth. It is interesting to note the occurrence of the ores 

 imniediately beneath very silicious layers at Mineville, but the 

 silicious or ''21 " gneiss as it now stands does not represent suffi- 

 cient normal syenite to have yielded the vast quantity of magne- 

 tite now found in the ore. The separation must have taken place 

 elsewhere. In a viscous flowage, it is conceivable that the bulging 

 folds might have been yielded under pressure, and some of the 

 difficulties afforded by such extreme local folding of sedimentary 

 rocks may be avoided. 



In June 1909 in the American Journal of Science, page 421, 

 F. E. Wright and E. S. Larsen published a very interesting and 

 significant paper entitled " Quartz as a Geologic Thermometer.'' 

 The point of importance is this. When silica crystallizes above 

 800° C. tridymite is the form assumed, but when it crystallizes 

 below 800° C. quartz is the result. Furthermore when quartz 

 develops between 575° C. and 800° C. it assumes one division of 

 the hexagonal system (apparently the trapezohedral-hemihedral) ; 

 while the quartz which forms below 575° C. falls in another divi- 



