350 A. C, Lane — White Mountain Physiography, 



must have gone down as well as back, and as the peaks 

 of the "White Mountains emerged as nnnataks, the White 

 Mountain massif must have been a pretty effective 

 obstacle to vigorous advance. At the same time the 

 disposal of a great ice sheet needs a milder climate than 

 that in which one would just appear. Thus we should 

 not then expect any local centers of glaciation, especially 

 when, as we shall see, the mountains were nearly a 

 thousand feet lower than at present. 



If, then, we state the history of the accordant levels in 

 the terms of Daly, the story would seem to run as 

 follows : 



Toward the close of the Paleozoic, the Appalachian 

 revolution, beginning in the Pennsylvanian, produced 

 great folding and an invasion of the Paleozoic sediments 

 by granites until they were altered so as to be nearly as 

 resistant to erosion as granites. Devonian black shales 

 were converted into chiastolite schists such as we find on 

 the Osgood trail of Mount Madison, Any accordant 

 levels produced by the 'limiting strength '' and ^^sostatic 

 adjustment" of this time were far above the present, not 

 less than 2000 feet above the top of Mount W^ashington. 



All the points ^' above the timber line," however, 

 passed into a zone of relatively vigorous erosion, and 

 may have been attacked by Permian glaciation. This 

 attack would be especially strong on the unmetamor- 

 phosed rocks and there would be a tendency to wear 

 down the ranges to a '^ rough accordance." When 

 erosion reached the deeper metamorphosed layer, it 

 would, as Daly says, go on more slowly. It seems to me 

 that I saw such a disproportionate abundance of porphy- 

 ritic marginal facies of granites, and of fibrolite, chias- 

 tolite, and tourmaline contact minerals, as to suggest that 

 erosion had not gone far below the ^' level of metamor- 

 phism" which, as Daly points out (op. cit., p. 116), may 

 be much less uneven than the folding surface. 



I think there are still traces of the folds in the 

 topography, of a synclinal from Littleton to Hanover, 

 and a shallower one, higher up on the general bulge, from 

 Goshen to Kearsarge, while the Presidential Range is 

 the stump of an anticlinal, left probably not as the relic 

 of an upfold, but as a more granitized and resistant core. 

 The long ridges of Jura or Allegheny type are gone, and 

 the very bottoms of the folds were higher than Mount 

 Kearsarge. But it looks as though the top of the meta- 



