GEOLOGY OF THE LAKE PLACID QUADRANGLE 35 



Outcrops seldom show a depth of weathering greater than a few 

 inches. Immediate surfaces are sometimes Hght gray due to leach- 

 ing out of the iron oxides by waters rich in decomposing organic 

 matter. 



The granularity varies considerably, in some places being rather 

 fine grained, and in other places being slightly porphyritic. Granu- 

 lation of the rock is often a notable feature, particularly when 

 viewed in thin section under the microscope. The feldspars show 

 the greatest effects of the crushing of the mineral grains. Notable 

 differences in coarseness of grain or degree of granulation are 

 sometimes very locally exhibited. 



The degree of foliation of the syenite varies extremely. Very 

 commonly the rock clearly displays a streaked or lerlticular 

 gneissoid structure which is accentuated by the arrangement of 

 the dark minerals with their long axes parallel to the foliation as, 

 for example, in the quarry at the extreme southern end of Lake 

 Placid. In other places it is excessively gneissoid as near the road 

 one-half of a mile north of Keene village, on the mountainside one- 

 half of a mile southeast of the mouth of Styles brook, and on the 

 mountain 13/2 miles south-southeast of Upper Jay. Notable varia- 

 tions in degree of foliation are often very local, sometimes showing 

 in single outcrops. The problem of the origin of the foliation 

 is discussed beyond under the caption '' Foliation." 



The usual range in the mineralogical composition of the normal 

 quartz syenite of the quadrangle is well shown in accompanying 

 table 2. Microperthite is the most abundant constituent, and it 

 occurs with orthoclase in about one-half of the slides examined. 

 Oligoclase and quartz in moderate amounts never fail. Horn- 

 blende, pyroxene and garnet usually occur in small amounts. Some 

 tiny grains or crystals of magnetite, apatite, and zircon almost 

 invariably occur. A few other minerals are sporadically present. 



