EOOFING SLATE. 



359 



The finest roofing slates of the Georgia slate period in Vermont, are found in Rutland 

 County. The excellent character of the slate for economical purposes is too well known to 

 demand repetition here. It has various colors, such as greenish, reddish-brown, what is 

 generally called " slate color," chocolate, mottled, bright red, bluish-gray. There are 

 numerous shades of all these colors as well as innumerable intermediate varieties. Some 

 of the varieties are so soft as to be used for slate pencils, and can be cut into every con- 

 ceivable shape. Many of the layers are compacted together, and, being destitute of cleav- 

 age planes, appear like a thick homogeneous mass of argillaceous rock. 



In Franklin County the clay slate of this series contains more silica than the same rock 

 in Rutland County. It may be particularly noticed at the locality of the Barrandia, etc., 

 in Georgia, where it is a black micaceous sandstone. It is micaceous also at St. Albans 

 village, and changes into novaculite schist in the town of Franklin. The true clay slate 

 seems to be developed in the east part of the terrain in the towns of Georgia and St. 

 Albans. Distinct clay slate is also found further north. 



Subordinate layers of rock associated with the clay slate in the southern terrain are the 

 following : Coarse harsh sandstone with angular grains cemented together by a paste 

 of chloritic aspect ; beds of gray sandstone ; green and black flinty slate ; blue compact 

 limestone; gray silicious limestone, and other limestones. In connection with the clay 

 slate there are often numerous veins of a fetid whitish quartz, full of angular cavities, 

 containing a brown residuum. 



The layers of quartz rock and sandstone are quite thin, and are found chiefly near the 

 upper part of the formation. In Rutland County the strata of quartz are interstratified 

 with the roofing slates in thin bands of a few inches in thickness. Sometimes they 

 enable us to ascertain the true planes of stratification in the slate, in distinction from the 

 planes of cleavage. 



Fio. 255. 



W 



Section at Barrett and Barnes' Quarry. 



Fig. 255 represents layers of quartz interstratified with clay slate, in Barrett & Barnes' 

 quarry on the west side of Lake Bombazine, in Castleton. The numerous fine lines in the 



