GEOLOGY OF FRANKLIN COUNTY 103 



gneiss is found from 2 to 3 miles below Tromblee's and is found 

 well exposed along Follensby pond. Going south, the last of it 

 is found in the gorge at Racquette falls. In all these places con- 

 siderable fairly coarse anorthosite-gabbro is found along with the 

 granular gneiss, and the only explanation that will fit the 

 phenomena in the writer's judgment is that the augen gneiss is 

 derived from the coarser rock by crushing. 



Whiteface type of anorthosite. Mt Whiteface in Essex county is 

 composed of a gabbroic rock of peculiar appearance, which has 

 been dubbed the Whiteface type by Kemp, to distinguish it from 

 the usual rock of the Mt Marcy type. 1 This rock gets over the 

 border into Franklin county at Franklin Falls, and also runs into 

 the corner of Clinton on Catamount and Wilmington mountains. 



This rock differs from the ordinary anorthosite in many re- 

 spects. It is usually completely granulated, though occasional 

 feldspar augen indicate a cataclastic structure. The feldspar is 

 white in color, the green tinge of the granulated feldspar in the 

 usual variety not appearing. The dark silicates are more promi- 

 nent, and the rock is usually markedly gneissoid. They are irreg- 

 ularly distributed, parts of the rock being nearly free from, and 

 parts heavily charged with them. The white color, even when the 

 rock is weathered, is in strong contrast to the green and rusty 

 brown shades of the gneissoid parts of the other rock. 



Under the microscope the chief difference is found in the pre- 

 dominance of hornblende among the ferro-magnesian silicates. 

 Next in abundance comes a green augite. No hypersthene has 

 been noted. The feldspar is mostly labradorite, as shown by 

 maximum extinctions of from 22° to 27° from the albite twining 

 plane in sections which extinguish equally on both sides. The 

 accessory minerals are the same as in the ordinary anorthosite, 

 iron ores, zircon, apatite, titanite, garnet, biotite and sometimes 

 a little quartz. The structure is cataclastic and the feldspars 

 show marked strain phenomena, the twining lamellae being bent, 

 often pinched out or else largely disappearing. In many slides 



iKerap, J. F. 15th an. rep't N. Y. state geologist. 1895. pt 1. p. 587. Ibid. 

 Bull. N. Y, state museum no, 21. 5:57. 



