ber:s^ardston series of upper devonian. 287 



The arg-illite, though the oldest rock, is least luetainorphosed; it is 

 crumpled and cleaved with dull surfaces and is full of coal grains and 

 kaolin, in its most eastern exposures showing minute pustules on its slaty 

 surfaces, and at last developing garnet and biotite in some abundanc-e. In 

 the western exposures of the Bernardston mica-schist series kaolin could 

 scarcely be detected, and biotite, garnet, and staurolite were quite abund- 

 ant but almost microscopic, while farther east the surfaces show clearly the 

 muscovite sheen and the above accessories are abundant and large. In the 

 Conway mica-schist, which lies below the argillite, the separate musco\-ite 

 scales are clearly visible to the eye, and the same accessories occur still 

 lai'ger and with a very ditferent and much more complex structure. 



PETROGRAPHICAL DESCRIPTION. 



THE QUARTZITE SERIES. 



1. Micaceous quartzite from South Vernon, roadside east of Lily Pond, 

 near the town line. A rather thin-foliated and somewhat fine-grained gneis- 

 soid rock, the broad and abundant films of a green micaceous mineral sepa- 

 rating the white, fine-granular quartzose ground. This is the Bethlehem 

 gneiss of Prof. C. H. Hitchcock.^ In section the quartz ground is plainly 

 clastic. The abvmdant scales of biotite are rarely brown at center, but mostly 

 changed to green, and are much stretched, wrinkled, and raveled out. 



2. Another specimen from the same region, but nearer Lily Pond, has 

 much more the aspect of a quartzite, but with the lens abundant fresh 

 secondary grains of feldspar can be seen among the quartz grains, with 

 many small garnets, octahedi-a of magnetite, needles of tremolite, and, in 

 the foliation plane, scales of deep-green biotite. In section the qi;artz gi-ound 

 is plainly clastic, the feldspars secondary, inclosing many quartz grains. 



3. A specimen fi-om the roadside near the outlet of the same pond is 

 a similar rock, showing here and there large blotches of green mica scales. 

 In section the fine clastic quartz ground contains many magnetite and 

 garnet grains, fine filaments of tremolite with weak dichroism, biotite with 

 very strong dichroism, yellow and very dark oliA^e-greeu, the latter rarely 

 changing to a light-green chlorite. 



4. A specimen taken from a branch in the road between Lily Pond 

 and the limestone (north of E. Tylor's) is of less granular texture than the 



'Geological map of New Hampshire, 17, atlaa. 



