C. L. Whittle — Main Axis of the Green Mountains. 353 



lower rocks by no line of demarcation whatever — the two 

 formations possessing an induced structural conformity due to 

 dynamic processes. This conglomerate is by no means invari- 

 able in character, but is subject to great differences of habit. 

 Normally it may be described as a conglomerate-gneiss in which 

 more or less detrital material can still be seen. Its clastic 

 character may be entirely lost when it passes into a chlorite, 

 muscovite schist or when it is represented by a vitreous quartz- 

 ite or quartzite breccia. I have previously described an ottrelite- 

 bearing phase of this horizon.* It forms with the mica schist 

 the most persistent horizon in the pre-Cambrian rocks known 

 to me. 



This border series has been extended eastward nearly continu- 

 ously across the range to the Plymouth valley. A schistose 

 phase of the metamorphic conglomerate forms the summit of 

 JVTendon and Killington, two of the highest peaks in the State. 

 Blue liidge is capped by the same rock and the beautiful moun- 

 tain known as Pico is also surmounted by the same horizon over- 

 turned to the west upon the pebbly limestones. The limestones 

 having been eaten out on the west and southwest undermining of 

 the schist has taken place resulting in steep escarpments near 

 the summit. In a general way this is true of many of the 

 mountains in the heart of the range that have been examined by 

 me north of Mt. Stratton. The eastern slopes are commonly 

 much less steep than the western as would be the case were 

 the strata really dipping towards the east and no doubt the 

 topography is directly dependant on the eastward-dipping 

 schistosity. But it is noticable that it is not the general schis- 

 tosity that determines the positions of mountain crests but a 

 somewhat local one of more pronounced character developed 

 in the backs (east side) of overturned folds where, owing to 

 greater shearing and stretching the maximum schistosity is 

 developed, resulting in a belt of greatest resistance to erosion. 

 The schistosity planes on the backs of the folds have a gentle 

 dip easterly and consequently these slopes are comparatively 

 gentle ; the western slopes are often structurally infolded syn- 

 clinal troughs in which by the reversal of the geological series the 

 limestone belts occur with lower members above them. What- 

 ever member of the metamorphic series now occupies the 

 eastern or gentle slope of the mountains it is uniformly schis- 

 tose. Ascending any of the high peaks in Mendon or Sher- 

 burne from the west one encounters steep slopes and usually a 

 duplication of the infolded members of the series. In such 

 environment crinkling and crushing are most pronounced, — 

 the strata making the eastern slopes being much less crinkled 



* An Ottrelite-Bearing Phase of a Metamorphic Conglomerate in the Green 

 ^Mountains. This Journal, vol. xliv, 1892. 



