212 



R. PUMPELLY — SECULAR ROCK-DISINTEGRATION. 



President Edward Hitchcock had shown long ago the anticlinal structure 

 of this central ridge. 



In that part of this central ridge called Hoosac mountain, we find a cen- 

 tral mass of the old granitoid gneiss, a very coarsely crystalline rock with 

 one-inch to two-inch crystals of microcline, and blue quartz. This is over- 

 lain by the white gneisses and still younger schists, the whole forming a low, 

 broad anticlinal, whose axis pitches about ten degrees northerly ; while im- 

 mediately w^est of this arch, the whole series is pushed over toward the west 



'^/"^oJ^nV 



E. 





v/. 



-^W 



FiGUKE l—Section through Stamford Dike. 



W. 



•m^Mm 



Figure 2 — Plan of Stamford Dike. 



Cambrian conglomerate deposited in the washed-out fissure of a metamorphosed diabase dike 

 in granitoid gneiss. Near Stamford, Vermont. C = Cambrian {Olenellus) conglomerate deposited 

 in the fissure; c= Lower layers of conglomerate, rendered schistose through admixture of the 

 altered dike material ; d = Diabase of the dike, showing schistose metamorphism ; e — altered dike 

 material; g= Granitoid gneiss (pre-Cambrian). 



to make an overturned flat fold at the summit, and then to descend the west- 

 ern flank in a series of crumple-folds which are also overturned to the west. 

 The axes of all these folds pitch about ten degrees to the north. 



Toward the southern end, this lateral fold makes a remarkable turn to the 

 east, so that it is here pushed over to the south ; and in this overturn are 

 enfolded both the white gneisses and the schist. 



We have studied the mountain in detail, and find that the rocks surround- 

 ing the old granitoid gneisses, and included between it and the schist, are a 



