ALGONKIAN ROCKS IN VERMONT. 41 1 



have been developed, but the larger clastic feldspar may be still 

 detected in a fine-grained ground mass. On White Rock Moun- 

 tain its place is occupied by a well-marked sandstone carrying 

 some biotite. Microscopically the rock is made up essentiall}^ of 

 small grains of clastic quartz. The larger pebbles of quartz and 

 feldspar varying much in abundance in different localities. In 

 the heart of the range a gneissose phase is produced by granula- 

 tion and by development of pale-green, pleochroic muscovite 

 and glassy plagioclase from the feldspar pebbles. The mica in 

 the most massive phase is also green muscovite. 



Immediately below the quartzite are fifty feet of pebbly, 

 crystalline limestone, the pebbles being largely feldspar, like 

 those in the quartzite. A narrow valley occurs here in this sec- 

 tion due to the relatively rapid removal of the limestone. Nick- 

 wacket Mountain along its northern peak exhibits the best 

 development of this rock, where its thickness may be safely esti- 

 mated at 400 feet. It is only locally pebbly there in contact 

 with quartzose layers or the main body of the quartzite above. 

 Lack of persistence characterizes this work as one would expect. 

 This seems to be due to want of, or to differences in, original 

 deposition in many localities ; to its alteration to other minerals ; 

 to its removal by solution, and to its being squeezed out during 

 folding. The rock is locally graphitic and usually quartzose, 

 especially where it occurs in thin beds in the micaceous pebble- 

 bearing quartzite. Phlogopite is common in little flakes in some 

 dolomitic varieties. All through the mountains of the Rutland 

 Sheet it forms an easily-recognized horizon. Near the summit 

 of Pico peak, just north of Killington, it occurs, and by its rapid 

 removal it has given rise to escarpments on the southwest slope 

 of the mountain. 



Some fifty feet of green muscovite schist occurs next below, 

 which may be considered a laminated phase of the micaceous 

 quartzite which usually appears below the limestone. This 

 grades downward into a flinty quartzite along this section. 

 Locally the quartzite carries pebbles of quartz and as one goes 

 east it is seen to grade into the metamorphic conglomerate that 



