SILICIOUS LIMESTONE. 401 



t 



IV. & V. CLAY SLATE, TALCOSE SCHIST, TALCOSE LIMESTONE, ETC. 



So much clay slate is interstratified with the western belt of the Eolian limestone, that 

 it is impossible to include all the limestone under one color on the map, without including 

 much of the slate with it. This is the case between Fairhaven and the north part of 

 Orwell and Sudbury. The slate is all argillaceous, sometimes slightly argillaceous. It is 

 very remarkable that these slates should entirely disappear and be replaced by limestone. 



But elsewhere in Vermont, it is common to find occasional seams of slate interstratified 

 with the limestone. It is the most common north of the slates referred to, but is not 

 entirely wanting in the south part of the formation. The largest amount of slate we 

 have seen at any one locality, is at Weybridge, near the monument of Silas Wright. It 

 must be at least fifty feet thick, and is interstratified with limestone, and is about a mile 

 east of Snake Mountain. 



Layers of limestone are often separated from one another by argillaceous films. Often 

 these films become talcose, and even talcose schist. There is scarcely a marble quarry in 

 Vermont where beautifully crystalline seams of talcose schist do not occur. As the marble 

 is delicately white and clear, so the associated schists have a delicately distinct color and 

 are free from foreign minerals. Really, however, the schists appear like the impurities 

 of the marble collected together at intervals : as if the Maker of the marble had formed it 

 on purpose for man's use. With these schists limestone, more or less talcose, is associated 

 in small quantities. Specimens of some of these varieties may be seen in Nos. j^g, 

 s> iTO) ir> iio) an <l ^> i n the State Cabinet. 



VI. QUARTZOSE LIMESTONES, AND BEDS OF QUARTZ. 



Under this head we include all beds of pure silicious matter, and those varieties of 

 silicious limestone of which more than half are silica. Of pure layers of quartz good exam- 

 ples are found in Bennington, Manchester, Cornwall and Shoreham. Between the villages 

 of East Bennington and Bennington the quartz shows itself both upon the plain and 

 upon the hill. The rock is undistinguishable from the usual variety of the quartz formation. 

 The strata are about two feet thick. At Rich's village in Shoreham the layer of quartz 

 occupies the lower portion of the valley, and is about eight feet thick. Other similar lay- 

 ers occur to the east both in Shoreham and Cornwall. Beds of quartz rock are found in 

 the Eolian limestone at Factory Point in Manchester. 



Perhaps the range of quartz rock from Chittenden to Danby ought to be considered as 

 a part of the limestone, as it is interstratified with it. 



Much of the limestone immediately bordering upon the quartz rock is a calcareous quartz 

 rock. But the silica and carbonate of lime must be regarded as mixtures and not chemi- 

 cal combinations. So silicious are some of these varieties that some have called 

 them quartz rock, as along the eastern boundary of the limestone from Dorset to Danby 

 and W. Clarendon. At the latter place there is a calcareous sandstone interstratified with 

 the limestone, very much like some varieties of Potsdam sandstone except that the cement 

 of the grains of sand is calcareous. At West Dorset, in the great valley of the mountains 

 and also near the village, there is a red quartzose limestone, appearing as if it had been 

 severely heated. 



