106 GREEN MOUNTAINS IN MASSACHUSETTS. 



other conformably at so many points and to curve around in conformity, as at 

 the southwest corner of Hoosac mountain, no kind of fault could explain 

 the relations. In fact, faults on a large scale seem to be absent, although 

 considerable breaking may have accompanied the great crumpling. On 

 the summit of the mountain east of Berkshire, near the extreme southern end 

 of the map, a small fault was found between quartzite and schist. The 

 relation of the rocks at the west end of the tunnel is of much more impor- 

 tance and the explanation not easv without assuming a fault. It will be 

 noticed by Profile in, PI. v, that the west edge of the trough of schist 

 which runs along the west slope of the mountain lies at the tunnel level, con- 

 siderably west of its position at the surface, so that the band of white gneiss 

 lying in the tunnel west of the schist seems to lie on top of it at the surface. 

 It should be remembered that this band of schist and gneiss west of it have 

 been traced many miles side by side to the south point of the great fold, 

 where they curve together to the east and are found in conformable contact 

 and even transition with each other. It is therefore impossible to explain 

 their general relations by a fault, but there may be a fault separating them 

 for a short distance here or else an overturned fold in the western gneiss 

 curving far back to the east, like the great Grlarus fold. 1 It would be impos- 

 sible fully to explain by words the structure of the east to west striking 

 gneisses just south of the west corner of the main fold. If a piece of cloth is 

 worked into a number of parallel folds or plaits and one-half of the cloth bent 

 around at right angles to the former general trend of the plaits, we get just 

 the series of transverse folds which exist on the mountain. The sections of 

 the Alps given by Heim show folding of equal complication in younger 

 rocks. A model would be the proper means of representing this structure. 

 One result of this work important to future investigation in the regions 

 of crystalline rocks is that it shows the possibility, by proper methods of 

 work, of determining much of the stratigraphy of these rocks, improbable 

 as it may seem at first sight. The gneisses of the Green mountains are 

 just as susceptible to stratigraphic investigation as the unaltered sediments 

 of the Appalachians, but the problem is much more difficult owing to the 

 secondary structures produced by metamorphism. 



1 Heim, " Mechanismus <ler Gebirgsbildung." 



