GEOLOGY OF THE NORTHERN ADIRONDACK REGION 



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certainly, and in the former probably, there are granites of 

 more than one, perhaps of several different ages. The Grenville 

 and Saranac rocks have been already described. It remains to 

 consider the others. These appear in several forms, some fine 

 and some coarse grained, some almost lacking in dark colored 

 minerals and others comparatively rich in them, some repre- 

 senting well defined types which may be recognized anywhere, 

 while others are more indefinite and variable, and all are much 

 easier to recognize than to describe. 



Granitic phase of the syenite. In several localities syenite has 

 been noted passing into a red, granitic gneiss, as first shown by 

 Smyth for the Diana area. In all cases observed the transition 

 is gradual, and there can be no doubt of the unity of the two 

 rocks. The Tupper lake syenite shows changes of the sort most 

 excellently. The color change is gradual and intermediate rocks 

 of mottled green and red appearance are not uncommon. Such 

 are seen to good advantage in Litchfield park, where the numer- 

 ous rock ledges, often blasted, along the carefully constructed 

 roadways give exceptional advantages for observation. Quartz 

 increases in amount in these rocks while pyroxene commonly dis- 

 appears, being replaced by hornblende and biotite, usually in 

 respectable amount. No analyses have yet been made of these 

 rocks, and it may be that they do not quite reach a sufficient 

 degree of acidity to justify their being classed as granites, but it 

 seems that in large part they must do so, and they certainly 

 represent as great a departure from the normal syenite type in 

 one direction as the gabbroic variety does in the other. The 

 rock shows the same variations in coarseness and in presence or 

 absence of feldspar augen that the ordinary syenite exhibits. 

 There is also in some varieties the same tendency of the quartz 

 to assume the lens, or spindle form that is seen in the more 

 quartzose syenites. 



In going farther south this granitic phase of the syenite gives 

 place to an even more distinctly granitic gneiss, or rather gneis- 

 soid granite, in which frequent patchy outcrops of both ordinary 

 syenite and its granitic phase occur, and this rock extends out 

 beyond the limits of the district which the writer has studied. The 

 exposures have not been so situated as to permit of precise 



