274 J. W. GOLDTHWAIT GLACIATION IN THE WHITE MOUNTAINS 



ward, the dispersion of drift from northerly sources to southerly resting 

 places leaves little doubt concerning it. In fact, both Agassiz and Hitch- 

 cock, although firm advocates of the theory of local White Mountain 

 glaciers, accepted all the striae as records of the general southward move- 

 ment of the continental ice-sheet. It is of course true that a local ice-cap 

 on the White Mountains would be likely to have a border here, trending 

 northeast-southwest, since this is on the northwest side of the mountains. 

 The question whether the moraine marks a local ice-border or a part of 

 the Canadian ice-border, therefore, must be settled primarily by the direc- 

 tion in which erratic stones have traveled in the construction of it. 



SOURCES OF THE DRIFT IN THE MORAINE 



The difficulty of stating definitely the paths traveled by erratics is 

 even greater than Agassiz pointed out. In addition to the chance for 

 confusing an earlier, southeastward movement with a later, northward or 

 northwestward one — which might account for finding "very few cases of 

 their protrusion beyond their starting point"— there is the highly impor- 

 tant circumstance that a drift blanket covers a very large per cent of the 

 surface, effectively concealing the rock structure; and there is also the 

 fact that this structure consists of gneisses and other granitoid rocks 

 which bear resemblances to one another, while varying within themselves 

 in texture, structure, and composition. Within the district just described 

 Hitchcock recognized "Bethlehem gneiss," "Lake Winnepesaukee gneiss," 

 and "porphyritic granite," with small areas of "Coos mica schists" not 

 liable to be confused with the gneissic rocks. So far as the "Lake Winne- 

 pesaukee gneiss" is concerned, it seems to me that in this district it is 

 merely a border-zone facies of the "Bethlehem gneiss." It is a well 

 foliated biotite gneiss, similar in all respects to the border zone of the 

 "Lebanon granite" of Hanover, New Hampshire, which Hitchcock him- 

 self recognized as the counterpart of the "Bethlehem gneiss." The por- 

 phyritic gneiss is more distinct, carrying phenocrysts iy 2 to 2 inches in 

 diameter ; yet there is opportunity to confuse it with the more porphyritic 

 facies of the "Bethlehem gneiss." There appears to be ample opportunity 

 for disagreement in the discrimination between these structures accord- 

 ing to lithological composition. There is much greater cause for disa- 

 greement regarding the extent of surface which each type of rock occu- 

 pies, since, as already stated, most of the area is covered with drift. The 

 outlines of the several areas here, as elsewhere, on the geological map of 

 New Hampshire in Hitchcock's atlas of the State, are manifestly arbi- 

 trary and unnatural. Boundaries are drawn in arcs of circles or in 

 straight lines for distances of from 2 to 10 miles; plutonic masses are 



