GEOLOGY OF THE WHITE MOUNTAIN DISTRICT. 223 



sharp peak to the north of it before reaching the " Notch," or Mt. Lowell. 

 All these mountains are full of precipices, often inaccessible. In the 

 Pilot range so much debris has accumulated about the porphyry peaks, 

 that the ledges cannot be seen except very near their summits; and it is 

 for this reason that it has been so difficult to learn the relations existing 

 between this and the adjacent Huronian. 



There are a dozen different areas of rock in the White Mountain dis- 

 trict referable to this division, which I will describe under the following 

 names: i. Lafayette range. 2. Twin Mountain area. 3. Mt. Carrigain. 

 4. In Waten^ille and Albany. 5. Mt. Tom area. 6. In Bartlett, Jackson, 

 and Chatham. 7. Pilot Mountain range. 



The Lafayette Range. 



There is little to be added to the general statement, on page 220, 

 respecting the shape of this area. It is a narrow strip, about six miles 

 long, sometimes half a mile wide, from the north slope of Mt. Lafayette, 

 through Mt. Lincoln, the south peak, and Mt. Liberty to Mt. Flume. 

 Between the last two there is a marked curve to the east. The south end 

 of Mt. Flume is precipitous for several hundred feet. 



The saddle between Lafayette and Lincoln has been cut down to the 

 Albany granite, leaving upon the former mountain a porphyritic cap 

 about one hundred and fifty feet thick; and a small hummock in the 

 depression has only fifteen feet of porphyry upon it. Beyond it to the 

 south is a dyke-like felsite mass, thirty feet wide. On Mt. Lincoln the 

 porphyry seems to slope south-easterly about ten degrees. From this 

 peak to the south end of the ridge, the summit is entirely composed of a 

 dark-colored porphyry. At the south end the divisional planes slope as 

 before ; and, about three hundred feet down, on the south-west side, we 

 found exposures of compact labradorite. These figures may express the 

 thickness of the dark porphyritic cap. 



Direct observations between the south end of the Lafayette mountains 

 and Mt. Liberty are wanting. Liberty is capped by Albany granite ; but 

 we suppose its eastern slope is porphyry, which extends from the peak 

 south of Lincoln across to the pinnacle of Mt. Flume. It is at least six 

 hundred feet thick at the last named summit. (See vol. i, p. 42.) It is a 

 fact to be remembered, that where the uppermost part of the Albany 



