Page:The Journal of geology (IA journalofgeology21894univers).pdf/427

have been developed, but the larger clastic feldspar may be still detected in a fine-grained ground mass. On White Rock Mountain its place is occupied by a well-marked sandstone carrying some biotite. Microscopically the rock is made up essentially 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 granulation 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 section due to the relatively rapid removal of the limestone. Nickwacket Mountain along its northern peak exhibits the best development of this rock, where its thickness may be safely estimated 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