SECTION ACROSS THE GREEN MOUNTAINS. 37 



Myself and son, aided by the senior class of 1861 in Amherst College, have recently 

 (October 1860) traversed this line mostly on foot, and obtained, as the result, the section 

 below (Fig. 18) . The base of the section is the sea level, and the heights are laid off 

 from the same scale as the horizontal distance. This makes the Green Mountains (1390 

 feet above the ocean at Mount Holly) appear of very diminutive height. But it is a 

 true representation, excepting that the summit is a little too high in order to give the lines 

 distinctness. On both the flanks of the mountain the dips are quite distinct (they were 

 measured along the railroad from Ludlow to the summit as well as from the Plymouth 

 Ponds, and the mean taken), but in the central parts they are a good deal irregular. It 

 will be seen that all the central part of the mountain is gneiss of the peculiar kind 

 known as the Green Mountain gneiss. Above this lies what has been called talcose 

 schist, with which limestone is interstratified ; and on the east side several beds of dark 

 gray hyaline quartz, only a few feet thick. One of the beds, however, is snow white. 

 The upper part of the schist is the conglomerate already described, of a character so 

 marked as not to be mistaken. At the west end we found several beds of limestone, but 

 none of quartz. Beyond the conglomerate, however, and probably lying conformably 

 upon it, is an enormous development of granular quartz, which seems to have no coun- 

 terpart on the east side of the mountain. 



Fio. 18. 



ABC H it 



In this section a b shows the present surface, a being Wallingford, and b Plymouth. 

 From A to B we have the talcose conglomerate ; from B to C mainly gneiss, with some 

 schist, and at least three beds of limestone ; from C to D gneiss, with several trap dikes 

 at II, the summit level of the railroad ; from D to E gneiss, Avith taleose schist, and at 

 least two beds of limestone and several thin beds of quartz ; from E to F talcose con- 

 glomerate. This last rock, so distinct and peculiar, forms a good starting point for our 

 reasoning. I think no geologist will doubt that it once mantled over the mountains with 

 the subjacent strata, as represented in the above section. True we have not found all the 

 subordinate beds of limestone and quartz to correspond on the two sides of the mountain. 

 But there is a general correspondence. The beds of limestone, especially, may have 

 originally extended over the arch of the mountains, although it is not common to find 

 limestone beds as thin as these, with so great a lateral extension. And as to the beds of 

 quartz, if this be in nearly all cases a residuary rock, produced in the wet way, all we can 

 say is, that circumstances may have been more favorable for its production on the east 

 than on the west side of the arch of the mountain. 



Taking this section as a fair representation of the Green Mountains, several important 

 inferences follow. 1. It shows the gneiss of the Green Mountains to form a great anti- 

 clinal fold not a synclinal fold, as some have supposed. 2. This gneiss underlies the 

 talcose schist, the limestone, the quartz rock, and the conglomerate. 3. All these latter 

 rocks probably once mantled over the gneiss, though they have mostly disappeared 



