REPORT OF THE DIRECTOR I9IT 161 



of the gabbro nor its relation to the rusty gneiss could be determined 

 at this point. The section is diagrammatically shown in figure 26. 



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Fig. 26 Oie lenses more heavily shaded; gabbro hachured 



A massive rusty gneiss with much pyrite, which might be classed 

 as a second, but much lower grade ore body, underlies the main lens, 

 with a small barren space intervening. As indicated in the diagram, 

 it is thicker than the main lens, and much less sharply defined, 

 while at the same time the pyrite is very unevenly distributed. 



The gabbro above referred to is by far the most conspicuous rock 

 of the section and is best shown at the paper mill about half a mile 

 upstream from the first mentioned locality. The rock is very dark 

 in color, sometimes almost black, varying from medium to very 

 coarse in grain and from massive to strongly foliated. Abundant 

 mica, with a suggestion of flattened orbicular structure, gives to 

 some exposures a most peculiar aspect quite unlike that of any 

 rock seen by the writer elsewhere in the northern Adirondack region. 

 Farther upstream the rock becomes a rather coarse hornblende gneiss 

 whose origin would be very obscure but for the fortunate exposure 

 of the transitional belt between the two phases. 



While in the field the rock is conspicuously hornblendic and mica- 

 ceous rather than pyroxenic, thin sections of the more massive 

 varieties show sufficient pyroxene to indicate the probability that 

 this was the prevailing original ferro-magnesian mineral. For this 

 reason the rock is regarded as a member of the widespread gabbros 

 of the Adirondacks, rather than a somewhat pyroxenic diorite. The 

 gabbro, in its gneissoid phase, is extensively developed in the vicinity 

 and, while not yet mapped, covers some square miles. A consider- 

 able extension to the southwestward toward the Stella mines tends 

 to support the conclusion, previously referred to, that the very 

 similar hornblende gneiss at the latter locality may be_ in reality a 

 phase of this same gabbro. 



While at the lower end of the gorge at Pyrites the gabbro appears 

 below the ore only, south of the paper mill it occurs also as a thin 

 sheet above the pyrite formation, the main body continuing below. 

 This is best shown at the lower end of a small island in the Grasse 

 river just below the dam. Here the rusty gneiss, with abundant 



