328 VAKIETIES. 



formation, whose color varies between gray and chocolate, and contains many grains of 

 feldspar and other easily decomposing substances. 



North of Burlington this variety is mostly replaced by red and variegated dolomites, 

 which have been gradually increasing in amount north of Addison. At Milton a grayish 

 quartz rock appears, probably equivalent to the red rock. The red color is owing to the 

 change in the combination of the iron, produced by heat, as elsewhere. 



The other sandstones which lack the brighter colors are distinct from this variety in 

 their appearance. Sonic beds pass insensibly into a semi-vitreous sandstone, not distin- 

 guishable from the quartz rock at the western base of the Green Mountains. These beds 

 may be seen at Monkton, where it is difficult to draw the line between the red sandrock 

 series and the quartz rock, and in Franklin County, in the towns of Milton, Fairfax, 

 Georgia, and St. Albans. 



The characteristic beds of the second variety of sandstone are generally very thin from 

 two to twelve inches being interstratified with the red sandstones and dolomites. Hand 

 specimens cannot be distinguished lithologically from the Potsdam sandstone. Occasion- 

 ally there is a considerable thickness of it, as in Highgate, a mile south-east of Saxe's 

 mills, where it must be more than ten feet thick. These beds have probably confirmed 

 some geologists in their opinion that this rock is about the age of the Potsdam sandstone. 



Brecciated rocks are very numerous in this series, and there are several kinds of them. 

 A peculiar variety, represented by Nos. ^ and >, abounds in the east part of High- 

 gate, particularly at Highgate Falls. Prof. Emmons figured a specimen of it in the Geol. 

 Second Dist. JN". Y., page 322. The fragments are angular masses of slate, sometimes 

 weighing a hundred pounds, having their own planes of stratification distinct, but not ar- 

 ranged so that the planes of the fragments are parallel with the strata of the breccia. 

 There is a little carbonate of lime in portions of the breccia, as well as occasional travers- 

 ing veins of calcite, introduced after the formation of the rock itself. It is difficult to 

 imagine how this rock could be formed, and yet preserve so perfectly all the delicate 

 angles of the fragments. This breccia is remarkably compact. It is not found south of 

 Highgate. Further south, near the Lake shore, in Georgia, Milton, and Colchester, the 

 breccias are dolomitic. In Colchester they form a beautiful marble, which is well repre- 

 sented in the State Cabinet, and known as the red, mottled and variegated marbles of 

 Colchester or Burlington. 



Further south the breccias diminish in quantity. In the north part of Monkton, Nos. 

 ifa to jfg were obtained of an indescribable but very beautiful variety, intermediate 

 between Nos. -jg and 3^, and some forms calciferous sandrock. 



Most of the varieties of this formation are more or less calcareous. Hence the varia- 

 tions observed in the fourth variety are very great, and are not generally worthy of 

 specification. In Highgate, where this formation is best developed, the prevailing rock 

 is a dark brown, massive, impure limestone, forming numerous small hills with mural 

 sides. This calcareous rock continues to Burlington, where it is interstratified with sand- 

 stones. In Georgia and Milton, this variety becomes a calcareous sandstone, closely 

 resembling the calciferous sandrock of the Lower Silurian. In Hinesburgh, Monkton, 

 etc., there ai-e beds of limestone, occasionally nearly pure carbonate of lime, as at Hines- 

 burgh Center, where some of it is manufactured into quicklime. We think it not unlikely 



