286 J. W. GOLDTHWAIT GL'ACTATION IN THE WHITE MOUNTAINS 



The evidence here is purely and simply the presence in the Ammonoosuc 

 Valley of small morainic deposits. Hitchcock's description of them does 

 not afford ground for choosing between the theory of a local valley glacier 

 and that of an ice-sheet. In the field one finds that the latter theory is 

 entirely satisfactory. 



"In the fields east of the Twin Mountain House there are hundreds of 

 boulders of Mount Deception granite, often 12 feet in length. . . . 

 This is an example of materials transported westerly a distance of four 

 miles." This evidence has been discussed on an earlier page, where the 

 full quotation appears. The parent ledges in question lie up the hillside, 

 a quarter of a mile northwest of the blocks, and bear striae which were 

 made by the southeastward movement of the Canadian ice-sheet. More- 

 over, the evidence from the Carroll outwash plains and kame terraces, 

 near by, as already explained, argues against the theory of a local Ammo- 

 noosuc glacier. 



"Just west of Rouiiseval and Colburn's sawmill, midway between the Twin 

 and White Mountain houses, I found a large block of granite, in 1871, nearly 

 12 feet in diameter, and about square, closely resembling a handsome variety 

 of granite occurring on Mount Willey and further south. A second small one 

 exists in the neighborhood. I have never found this particular kind of granite 

 north of the Notch in ledges, and as it occurs with the Conway granite near 

 Mount Willey, it is probable that these blocks descended the Zealand Valley, 

 starting from the west side of the same mountain." 22 



The value of this evidence is not easy to estimate, since Hitchcock did 

 not describe the variety of Conway granite in question, and it can not 

 therefore be identified, either at the alleged source on Mount Willey or 

 in other districts of Conway granite. Hitchcock maps an area of Conway 

 granite immediately north of the place where the boulders were reported. 

 After seeing the mistake which he made in overlooking the ledges of 

 granite on the hill east of Twin Mountain (discussed on page 25), one 

 may reasonably question whether the peculiar Conway granite boulders 

 near the Eounseval sawmill may not have come from the area of Conway . 

 granite north of that point, instead of from the southerly exposure of 

 Conway granite on Mount Willey. To assume that the "handsome va- 

 riety" observed in the boulders does not occur in the more northerly area 

 because it has not been seen there is unwarranted. The areal geology of 

 that wooded and drift-covered country was very imperfectly known in 

 Hitchcock's time, as now. The real source of the boulders in question 

 must remain in doubt. 



"Other boulders, seemingly from the south, are a few of Chocorua granite 

 from near the Crawford House, in which Professor Dana discovered grains of 



22 Loc. cit. 



