C. L. Whittle — Main Axis of the Green Mountains. 351 



schists, etc., etc. The micro-structure of all the core rocks 

 attest the pressure brought to bear upon them by the granu- 

 lated condition of their quartz and feldspar constituents — a 

 feature which is strongly contrasted with the less-sugared 

 and more modern appearance of the border series. The 

 rocks of this area are less schistose ; biotite seems to re- 

 place muscovite or sericite of the border metamorphics ; 

 gneisses are more dominant and the border regional cleavage 

 of N . 10°-15° E. is not nearly so pronounced. In place of this we 

 find a more coarsely crystalline structure — the structure being 

 due more to an apparent rearrangement of their mineral con- 

 stituents than to a development of mica along planes of shearing. 

 This banding is lacking in any uniformity of trend and is 

 strongly at variance with the persistence observed in the direc- 

 tion of the schistosity of the border : east and west strikes of 

 lamination are perhaps as frequently met with as those trend- 

 ing north and south, and the dips are equally variable. 



The upper part of the Algonkian or border series affords 

 evidence of at least two periods of orographic disturbance; 

 microscopic data for this the writer outlined in a bulletin of the 

 Geological Society of America.* This evidence is based on the 

 development of ottrelite and albites in the metamorphic conglom- 

 erate. These minerals as they grew include the crushed quartz 

 and feldspar mosaic resulting from an earlier period of environ- 

 ment produced in part by folding. In turn the ottrelite and albite 

 are occasionally bent and fractured evidencing a second period 

 of disturbance less violent than the first. Structurally we 

 have stronger evidence furnished by a conglomerate gneiss at 

 North Sherburne where an anticlinal axis trending about 25° 

 west of north represents the first period of disturbance ; a 

 later one induced in the rock the regional schistosity of the 

 range striking, as mentioned above N. 10°-15° E. Other 

 periods of folding in this series have probably taken place but 

 the data for their detection are not at hand. The lower rocks 

 of the Mt. Holly-Shrewsbury area must have experienced 

 even greater mutations. The greater granulation and litho- 

 logical differences observed and character of the folding may 

 be cited as evidence in support of such a belief. 



Mr. Wolff describes a northerly pitch in the crystallines of 

 the New Jersey Highlandsf and I have observed with him the 

 same pitch of the rocks of Hoosac Mountain. In general the 

 minor folds of the Green Mountains in the area described 

 above have the same gentle, northerly pitch. In a large way 



* Some Dynamic and Metasomatic Phenomena in a Metamorphic Conglomerate 

 in the Green Mountains, vol. iv, pp. 147-166. 



f "The Hibernian Fold," read before the Geological Society of America at the 

 winter meeting held in Boston, Mass., in December, 1893. 



