36 PHYSICAL GEOGRAPHY. 



up from below. As it contains no fragment of the common or trachytic granite, 

 we have concluded it to be more ancient than either of these granites, but newer 

 than the porphyritic gneiss. The two areas are also probably connected beneath the 

 Pemigewasset valley, under the common coarse granite, which either flowed in above 

 the breccia, or was deposited upon it quietly in some other way. 



8. Norian. This includes several areas of labradorite rock, including compact 

 felsites, breccias, and sienites. They are the Lafayette range, Twin Mountain area, near 

 Loon pond, Trypyramid region, Carrigain district, north of Mt. Tom, valley of Dry 

 river, valley of Rocky Branch, Sable mountain in Jackson, Mt. Pequawket or Kiarsarge, 

 Deer River valley in Albany, near Mt. Chocorua, and Red Hill, Moultonboro'. There 

 are other areas to be referred to the same group outside of the White Mountain area. 



9. Clay slate and Quartzites. The first of these areas is a limited one on the 

 south slope of Pequawket ; the second south-west of Mt. Willard, passing into andalu- 

 site slates and quartzites on Mts. Willey, Field, and Tom. 



10. Coos Group. This embraces the andalusite slates on the east flank of the Mt. 

 Washington range, repeated on the north-east side of Pine mountain, near Gorham, 

 and the staurolite rocks from Littleton southwards, curving around the underlying 

 Bethlehem gneiss. Only the eastern border of the latter is indicated upon the map. 



WHITE MOUNTAIN EXPLORATIONS IN 1872 AND 1873. 



A still larger party was organized for work in 1872. Under the direc- 

 tion of J. A. Leach, of Nashua, a plane-table survey was made of the 

 south-west portion of the mountain area, with the design of perfecting 

 the map. The rest of the party examined the rocks along the Saco val- 

 ley and in Albany for a period of three weeks, under the guidance of Mr. 

 Huntington. The explorations served to confirm the theory of the pre- 

 vious year concerning the arrangement of the formations. The parties 

 consisted of the following members of the class of 1872, Dartmouth col- 

 lege: E. J. Bartlett, W. H. Cotton, L. G. Farmer, G. H. Fletcher, A. M. 

 French, G. M. French, W. H. Galbraith, W. A. Holman, E. D. Mason, C. 

 H. Sawyer, H. M. Silver, G. F. Williams, and T. W. D. Worthen; N. W. 

 Ladd and A. O. Lawrence of the class of 1873. 



In 1873 a few points about the mountains were visited by Mr. Hunt- 

 ington and myself for the sake of completing our knowledge of them. 

 The exploration, so far as it seemed advisable to proceed with our present 

 instructions from the state authorities, had been essentially completed 

 in 1872. 



