202 GEOLOGY OF OLD HAMPSHIEE COUISTTY, MASS. 



The argillite is characterized by a great abundance of quartz nodules 

 and bosses, often of great size, which, though not wanting in the Bemards- 

 ton series, are there comparatively unimportant. 



On the road from Grreenfield to Charlemont, above Fall River bridge, 

 the argillite is a fine-cleaved roofing slate for a long distance by the road- 

 side, almost as fine a slate as that at the Gruilford quan-ies in the town next 

 north in Vennont. 



QUAETZITE IN THE ARGILLITE. 



On the road north from Bernardston, at C. Cushmore's, is a heavy 

 layer of a dark, thick-bedded quartzite about 33 feet thick, and a little far- 

 ther north, at I. K. Brown's, is a crumpled, thin-bedded quartzite. 



Just over the State line to the north, near the Guilford slate quatTies, 

 the argillite is replaced by a tine-grained quartzite, which President Hitch- 

 cock called a novaculite-schist and found to be a quarter of a mile thick.' 



PETROGRAPHICAL DESCRIPTION. 



The mass of rock is made up of minute, elongate, brightly jjolariziug 

 muscovite microlites, often raveled out at the ends and with wavy sides, in 

 an amorphous background. Clay-slate needles are only doubtfully present. 

 Stout elongate forms, opaque by transmitted and curdled white by reflected 

 light, seem to be leucoxene derived from menaccanite. Magnetite and 

 calcite are wanting. There is much coaly matter in swarms of black 

 dots, and rarely a biotite scale placed in the plane of cleavage. Often a 

 strongly marked pseudo-fluidal structure, expressed b}- the position of the 

 elongate muscovite crystals, indicates cleai-ly the mode in which pressure 

 has produced this cleavage. 



Microscopically the rock is thus a very fine-grained, argillitic mica- 

 schist or phyllite, and it differs much from the true argillites, e. g., the 

 cleaved slates of Snowden, Wales, or the slates of Hoosick Falls, New 

 York, with which I have compared it. I have followed custom in applying 

 the name argillite to the band of rock, somewhat in a geological sense. 



The rock sometimes contains small garnets in considerable number, and 

 these are often changed wholly or partly into small white balls of kaolin, 

 or kaolin and hematite. The kaolin was infusible and gave blue color with 



'Vermont Report, Vol. I, 1861, p. 490. 



