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



Lower Cambrian quartzite and limestone occupy the Rutland 

 valley. The quartzite lies at the base and is next above the 

 series of metamorphosed elastics lying between it and the still 

 more metamorphosed core of the range.* Plymouth valley is 

 also occupied by limestone which extends north to North 

 Sherburne, but its age is undetermined. Field evidence points 

 strongly to its equivalence to one of the limestones in the 

 metamorphosed elastics mentioned above occurring on the 

 west side of the range. 



The rocks of the range below the Olenellus horizon seem 

 to fall into two groups. 1, a border series consisting alone, so 

 far as I am aware, of metamorphosed sediments ; and 2, a core 

 series more metamorphosed, differing lithologically and carry- 

 ing igneous rocks antedating the border series. When one 

 first visits the eastern or western border of this area he is at 

 once struck by the great variety of rocks and the apparent 

 simplicity of their structure. Throughout the border areas the 

 strike of the most prominent structure is commonly N. 10°-15° E. 

 (magnetic) and the dip is generally steep easterly. This strike, 

 as is now well known corresponds to the trend of the main 

 Appalachian folding in New England. Further study of the 

 rocks shows its secondary nature, traversing as it does rocks of 

 the most varied texture and composition regardless of the real 

 stratification, now usually not decipherable, but in many places 

 still present where it has escaped the destructive dynamic 

 action to which the rocks have been not only once but several 

 times subjected. It is easy to be misled by this lamination 

 and it soon became apparent that where the structure seemed 

 the simplest in reality the obliteration of old bedding planes 

 is the most complete. One of the best examples of this is 

 seen at East Clarendon just north of where the Central Ver- 

 mont railroad enters Mill River valley after leaving the Rut- 

 land valley. Here the rock, a metamorphic conglomerate in 

 places is apparently as evenly-bedded as a Tertiary sandstone, 

 but close inspection locally shows that most of the smaller 

 pebble-like areas of quartz lying along the planes of schistosity 

 are really sheared areas of quartz derived from genuine peb- 

 bles. The plane of shearing crosses the pebbles diagonally ; 

 by granulation of the several parts of the faulted elastics 

 pseudo-pebbles lying parallel to the schistosity are produced 

 which in cross section strongly resemble ordinary waterworn 



* Id a paper that will soon appear in the Journal of Geology on "The Occur- 

 rence of Algonkian Rocks in Vermont and the Evidence for their Sub-Division n 

 the writer will call these upper metamorphic rocks the Mendon series. The 

 Mendon series is thought to lie discordantly above a still more metamorphosed 

 series in the core of the range that will be designated as the Mount Holly 

 group. 



