332 



stream continues westward in a deep valley for twenty miles, to 

 Hoosac mountain, before turning northwards. This valley has 

 probably been excavated in like manner ; but no exact measure- 

 ment can be made of the amount of erosion, because the river 

 crosses perpendicular strata. A line drawn from the summits on 

 either side of tlie valley to each other would give large results ; 

 but they would not be equal to the truth. 



Let us now look at the first described erosion in another light. 

 The gneiss rock at the bottom is exposed over an oval area about 

 three miles by two. If ten observers should start from the cen- 

 tre of the oval, and travel in as many different radiating direc- 

 tions, they would all see the same succession of rocks, and in the 

 same order. The dip is quaquaversal, gradually returning to an 

 anticlinal axis at a few miles distance north and south. Hence 

 there has been a cap denuded, three fifths of a mile thick. Doubt- 

 less, all along this anticlinal axis, wherever the upper rocks have 

 been removed, the gneiss beneath will be discovered. It corre- 

 sponds to the gneiss and hornblende slate of eastern Hampshire 

 and western Worcester counties, and would seem thus to lie 

 below the Metamorphosed Silurian rocks. If so, it should be 

 included among the Hypozoic rocks. 



Sections similar to the foregoing have been measured and de- 

 scribed by English geologists. Not being aware of any similar 

 work in our own country, I have described this section in hope 

 of drawing attention to the subject, and thus insure descriptions 

 of sections far more grand and interesting. I can vouch, on the 

 part of the Vermont survey, for a careful attention to this subject. 



Prof. W. B. Rogers made some remarks upon the section ex- 

 hibited by Mr. Hitchcock, which he characterized as a good 

 example, in a highly metamorphic region, of the prevailing struc- 

 ture of the Appalachian chain. He described the gradation from 

 closely folded curves to normal and flattened arches, which is so 

 beautifully displayed throughout this belt from Pennsylvania to 

 middle Alabama, and referred to the presence of like features in 

 the northern extension of the belt, as well as in the zone of 

 highly altered rocks adjoining it on the southeast. 



With respect to the break in the middle of the section pi-esent- 

 ing the character of an anticlinal valley, he remarked that this 



