GEOLOGY OF THE VICINITY OF LITTLE FALLS 85 



garnetiferous gneiss outcrops, whose relationships are also 

 uncertain. 



One quarter mile to the eastward, along the strike, are out- 

 crops of apparent syenite gneiss, but just north, massive ridges 

 of Grenville gneisses cut it out, and just south are granites and 

 dubious gneisses which are certainly not referable to the syenite, 

 so that we are dealing here with an exceedingly small syenite 

 intrusion, if it really be that rock. 



The ore itself is of the platy sort, rather than of the granular 

 crystalline character of much of the magnetite of the eastern 

 Adirondacks. In this respect it is like much of the Franklin 

 county ore. Now, while the writer has had no opportunity care- 

 fully to investigate these ores, the small study that he has been 

 able to give them leads to the belief that many of them are of 

 igneous origin, being basic segregations from the syenite magna, 

 just as the titaniferous magnetites are segregations from the an- 

 orthosite. But, whereas ores of the sort are quite customarily 

 developed in gabbro intrusions, they have been seldom noted in 

 syenites, so that the matter requires thorough investigation, and 

 the statement of origin is only tentatively advanced. The Salis- 

 bury ore also seems to fall into the same class, but, because of 

 the poor exposures and the very small size of the mass of ap- 

 parent syenite, the writer rather hesitates to advance the idea, 

 though himself rather confident of its verity. If the mass be a 

 result of differentiation in an intrusive, it is remarkable, not only 

 because of the kind of rock involved, but also because of the great 

 amount of differentiation in a very small eruptive mass. The 

 thin sections seem to bear out the idea of the igneous nature of 

 the whole, as will be shown later. 



PETROGRAPHY OF THE PRE-OAMBRIAN ROCKS 



Grenville rocks. These are old aqueous rocks which have been 

 so excessively metamorphosed as to have become entirely re- 

 crystallized, with loss of all original structures, so that the main 

 argument for their origin is that based on composition. As 

 occurring in the district, they consisted mainly of shales and 



