144 NEW YORK STATE 1 MUSEUM 



incomplete in some parts of the town, though general experience 

 so far as hitherto gained, has indicated a decrease, if not a failure, 

 of dikes in the southern central and southwestern crystalline areas. 



Series 1. Gneisses. The rocks of this series are much the 

 most important of all and constitute almost the entire area. 

 Several different varieties of gneisses are recognizable. The most 

 widespread is one typified by specimen 179, from the hills to the* 

 west of Wells village. It is a rock that is greenish when fresh 

 but red when weathered. The chief minerals are biotite, ortho- 

 clase, quartz and plagioclase. Garnet is abundant, and pegmatite 

 streaks run through the outcrops. This particular rock bears 

 witness to fairly severe dynamic metamorphism, but others have 

 Buffered much more and still others less. No. 170 is a granite not 

 very badly crushed, while 169 and 172 are of the same general 

 composition but are rolled out into thin layers. No. 174 al- 

 most if not quite approximates a schist, and under the micro- 

 scope displays biotite, quartz, plagioclase, orthoclase and garnet, 

 granitic gneiss, and must lie along some old fault line or line of 

 crushing. No. 176 is a syenitic gneiss, and under the microscope 

 exhibits orthoclase, microperthite, strained plagioclase and horn- 

 blende. No. 220 just on the ridge northeast of Wells village is the 

 same. 



In the hornblendic gneisses are bands of nearly pure horn- 

 blende, which may contain pyrite. These bands may be several 

 feet thick. One of exceptional persistence is exposed at locality 

 178. They are always parallel to the foliation both in dip and 

 strike, and, if they are sheared trap dikes, the foliation has been 

 induced in a direction parallel to the original strike of the dike. 



The strike of the gneisses is prevailingly northwest and south- 

 east, but it shifts occasionally even to a bearing at right angles 

 with this. Changes in the direction of the dip are also often 

 observed. 



The gneisses are extensively jointed, and often exhibit emphatic 

 escarpments along the line of the major joints; still it is not easy 

 to discriminate these steep cliffs from fault scarps. Just to the 

 northeast of Wells village the joints run n 80 e and n 15 e true 

 bearing, and the former gives rise to cliffs and ledges. 



