268 SMYTH — ROCKS OF NORTHWESTERN ADIRONDACK REGION. 



is in small tongues or veins there is a marked tendency for them to follow 

 the lamination of the gneiss, producing structures precisely like those 

 described and figured by Lehmann * in the case of similar intrusions 



occurring in Saxony (see figure 2). At many of 

 the exposures abundant inclusions of gneiss in 

 granite give further evidence of intrusion. 



While these relations are most extensively 

 shown in Pitcairn, indications of the same sort 

 may be found in Diana, particularly just north 

 of Harrisville, north of Indian lake, and two 

 miles east of Natural Bridge, on the Bonaparte 

 road. 



Thus it is evident that the limestone belts of 

 Antwerp-Gouverneur and of Diana-Pitcairn are 

 separated by a gneissic area whose southern 

 border is made up largely of intrusive rocks. 

 How much of this area is but a continuation of 

 the intrusions can be determined only by very 

 close and careful study, and perhaps not even 

 then ; but the facts at hand are certainly suggestive and seem to point 

 out a fruitful line of inquiry. 



Figure 2. — Granite Veins paral- 

 lel to Lamination of Gneiss. 

 The drawing is from field 



sketch made one mile north of 



Pitcairn Forks. 



Gabbros. 



FIRST VARIETY. 



Area of Occurrence. — Of gabbros there are three varieties, the most im- 

 portant being of somewhat exceptional character, which renders its 

 affinities rather uncertain. 

 The most typical gabbro oc- 

 cupies an area of hardly 

 more than a square mile, just 

 east of the village of Pitcairn, 

 or, as it is called more com- 

 monly by the inhabitants, 

 Geers. The southern edge 

 of this area is marked by a 

 steep cliff, like that formed 

 by the granite and gneiss j ust described. The two cliffs are almost in line, 

 though not continuous, and the structural relations of both are very 



* J. Lehmann : Untersuchungen uber die Entstehung der Altkrystallinisehen schiefer Gesteine, 

 p. 20. 



Figure 3.— Basic Gabbro cutting Limestone and Gneii 

 Diagramatic section of exposure at Pitcairn. 



