THE HOOSAC SGUIST. (37 



THE MONROE AREA. 



Prof. 0. H. Adams inrroduced the mime Green Mountain g-neiss for 

 the gneiss of the Grreen Mountain range in Vermont, in liis tirst report/ Init 

 without definition or detail. The name occurs in his enumeration of the 

 primary rocks, between talcose slate and gneiss proper, and he remai-ks that 

 in and south of Mount Holly the gneiss replaces more or less the talcose slate. 



In the second report of Professor Adams" is a letter from President 

 Hitchcock, who calls attention to the fact that the broad baud of gneiss 

 which makes the axis of the Green Mountains across Vermont seems in 

 Massachusetts to be replaced suddenly by mica-slate, and fears an appear- 

 ance of discrepancy between the niaps of the two surveys if the gneiss is 

 made to run up to the south line of Vermont. He expresses the belief tliat 

 the rocks change on the strike in the neighborhood of the State line, and 

 adds that much of the rock is halfway between gneiss and mica-slate. 



In his own final report on the geology of Vermont^ President Hitch- 

 cock says that Professor Adams gave the above name to distinguish from 

 true gneiss this range of gneiss, which is characterized by a deficiency of 

 feldspar, so that the rock is often mica-schist, or at the best feldspathic 

 mica-schist. 



On a later page* reference is made to the sudden change of the Green 

 Mountain gneiss into the gneiss and mica-schist of the Hoosac range, and 

 this change is explained thus: 



1. The mica-schist of Hoosac :Mouiitaiu aiul the gueiss of the Green Mountains 

 belong to the same formation, and the Massachusetts stratum of mica-schist becomes 

 gneiss extremely near the State line by the addition of a little feldspar. It is a case 

 of the metamorphism of one rock into another. 



iJ. There is a narrowing of the formations very near the State line. Botli the 

 gneiss formation and the mica-schist curve to the westward, so that in Massachusetts 

 the mica-schist and gneiss are narrower than in Vermont. 



It will be seen below that the Green Mountain gneiss in Heath and 

 Monroe dips beneath and does not pass into the mica-schist of the Hoosac 

 rauffe. 



' First Ann. Kept. Geology of Vermont, 1845, p. 62. 

 - Second Ann. Kept. Geology of Vermont, 1846, p. 248. 

 sRept. Geology of Vermont, Vol. I, 1861, p. 454. 

 ^Ibid., p. 462. 



