AMOUNT OF EROSION. 



223 



thickness of the different strata and get their true dip, we might by protraction find out 

 what thickness had disappeared from the present surface. 



FIG. 110. 



Fio. 110 (bis.) 



One of our number (c. H. H.) has attempted this, as well as the limited time at his 

 command would permit, with the following results : 



Thickness of the Gneiss that has disappeared, 951 feet, 

 do. of the Hornblende Schist, . ; 2640 feet, 

 do. of the Mica Schist, . . . 3933 feet. 



Total thickness, 7524 feet, 



or not far from a mile and a half. 



On Section I, this same anticlinal probably shows itself; at least the hornblende schist 

 appears ; but there the difficulties are still greater as to measurement. Still further to the 



southwest, however, at Shelburne Falls, 

 in Massachusetts, a few miles south of the 

 Vermont line, the same anticlinal probably 

 is brought to light more satisfactorily, 

 as is shown in the adjoining section (Fig. 

 110 bis.) c. H. H. devoted more time to 

 this case, before commencing the Vermont 



Survey, and found that nearly 10,000 feet have disappeared from the valley of Shelburne 

 Falls ! 



In South Wales the erosion was as much as 10,000 feet, according to Prof. Ramsey, and 

 his sober conviction was, that more land has disappeared from the island than now 

 remains above the waters. "We do not doubt that the same is true of New England. 

 But it demands much time to work out the problem fully, among our metamorphic rocks. 

 It is certainly a grand subject, and its solution would richly repay long and laborious 

 research. An inspection of our sections will show many places where anticlinals exist, of 

 such" a character as to afford a fair opportunity for measurement, though we think it 

 probable that the disturbed fossiliferous rocks of our country present a more promising 

 field. 



