42 



PHYSICAL GEOGRAPHY. 



Discovery of the Succession of Members of the Labrador System. 



The same report contains the announcement of the discovery of the 

 relations to one another of the several members of the Labrador group, 

 and also to the underlying porphyritic gneiss, White Mountain series, and 

 brecciated granite. 



From a peak north of Mt. Lafayette in Franconia to Flume mountain, 

 there seems to be a nearly continuous band of dark, compact feldspar, 

 about five miles long, and never more than two hundred to three hundred 

 feet thick. It closely resembles some of the compact labradorites. The 

 layers are horizontal, or nearly so, resting upon trachytic granite through- 

 out. It has not actually been traversed from the south end of the 

 Lafayette ridge to Flume mountain, but the topographical features of the 

 country are such as to render probable its contintiance by a curve to 

 connect with that which has been observed upon the latter summit. 

 The annexed wood-cut will show the relative position and thickness of 

 the rocks between Mt. Liberty (C) and Mt. Flume (A), two thousand 

 two hundred and fifty feet above the bottom of the valley. There is the 

 common coarse granite at the base, the celebrated Flume of Lincoln 

 (Franconia), lying at the bottom of the valley (F in the figure), eighteen 

 hundred and forty-nine feet above the ocean. Above the Pemigewasset 

 river there may be six hundred feet thickness of this rock, considering it 

 to lie horizontally, before reaching the trachytic variety. This in turn 

 may be one thousand feet thick, as shown at band C. This rock caps 

 Mt. Liberty, but the compact feldspar has been spared by the denuding 

 agencies upon Mt. Flume. As seen by the general map, the edges 

 of this dark rock everywhere rest upon the trachytic granite. 



Fig;. 2. 



Fdsite. 

 Trachytic Granite. 



Common Granite. 



Section across the Flume. 



