-..'A VABIETIE& 



Qiefr 

 The following MB the varieties of gneiss 



L 



2. Granitic gneiss. 

 a HomHendic, 



4. Porpfayritic gneiss, 



5. Epidotic gneiss. 



6. Calcareous gneiss. 



7. Talcoae gneiss. 



8. Feldspar and quartz. 



9. Hornblende schist. 



10. Bed* of quartz rock. 



11. Bed* of dolomite and limestone. 



12. Beds of steatite, seipeiitme aiid associated rocks, 



13. Talcose atd cbolori te schist*. 

 14. 



15. Emite. 



The first eight ate properly varieties of gneiss, the last seren are properly associated rocks, of which 

 abets 9, 11, 12, and 14 wffl be folly treated of in the descriptions of these rocks hereafter in this part of 

 the Report. 



L GSEISS. 



The gneiss of Veimont is qmte variable m its appearaiic,j^ The variation may be in 



the schistose or laminar structure, in thepredominance of one of the composing ininer^ or m the coarseness 

 of the grains. The gneiss is generally schistose, or made up of folia of the different mineral*. Each layer 

 may be composed of subordinate folia, or else the whole layer may be entirely composed of a single mineral. 

 When the layers are severally composed of aggregates of the same mineral, the gneiss may be called 

 laminar. Layers of hornblende are often connected with this variety, insomuch that in many instances the 

 reek nay be regarded as composed of alternating layers of gneiss, mica schist, and hornblende schist. 



In some parts of the gneisi, Hack mica is the most abundant mineral, and thus the rock is mostly black 

 mica ; e. &, No. tV faw Cavendish. Or the mica may be green instead of black, as in No. V from 

 Cavendish. Or the feldspar may be green, as in No. A from Townshend; etc. The firmness or coarseness 

 of the crystals composing die gneiss, presents a great number of varieties to the eye ; bat none of these 

 are worthy of specification. The prevailing color of the gneiss is grayish white, bat there are multitudes 

 of exceptions. 



The greatest peculiarity in the gneiss of Vermont, and more particularly in the range composing the 

 Green Mountains, consists in the deficiency of feldspar ; so that the rock is often mica schist, or at the 

 best, feldspathic mica schist. Because of this peculiarity, Prof. Adams called this range of gneiss the 

 dree* Wmdain gwetw, in order to distinguish it from true gneiss. We do not think it necessary to carry 

 rt this distinction upon the map, partly because of die multiplication of colors necessitated by the alter- 

 nations of the two lands of gneks, bat chiefly because true gneiss is the prevailing rock upon this belt. 

 It is chiefly developed, however, in the south part of the State, while the feldspathic mica schist is more 

 abundant in the north part of the State. 



II. GRAXITIC GSEISS. 



This variety approaches very near to granite, and band specimens of the two rocks cannot be distin- 

 gnshed from each other. Even large areas of the rock itself can scarcely be distinguished from granite. 

 Bat a careful examination wfll generally disclose an obsolete parallelism of the mica. In accordance 

 with the views adopted in tins report respecting die origin of granite, it will fellow that the difference 



