GEOLOGY OF THE WHITE MOUNTAIN DISTRICT. 105 



to the best aclv^antage.* Later observations, while modifying certain 

 features of the geographical distribution, and adding new areas to the 

 map, have tended to confirm this original impression. 



Inasmuch as the typical area of the Bethlehem gneiss lies partly in 

 three different topographical districts, though principally in the one now 

 under discussion, I have thought it best to describe it entirely in this 

 place. It occupies portions of the towns of Carroll, Whitefield, Beth- 

 lehem, Franconia, Littleton, and Lisbon. The specimens, however, arc 

 grouped geographically in the White Mountain and Ammonoosuc, as 

 well as the Coos and Essex, special collections. The references will be 

 made to them clearly enough to avoid confusion. 



The most characteristic of the rocks composing this formation is a 

 reddish granitic gneiss, the flesh-colored orthoclase predominating, with 

 chloritic or some hydro-micaceous mineral in place of ordinary mica, and 

 amorphous quartz in variable proportions. When this is not present it is 

 not easy to say that the finer-grained gneiss associated with it necessa- 

 rily belongs to this geological horizon. This second variety is like the 

 finer gneisses of the Montalban group. A third variety is a porphyritic 

 gneiss, sometimes suggesting the older group just described. It differs 

 from that in having smaller crystals of feldspar, which are arranged in 

 nodular bunches in the midst of the finer micaceous layers of the rock. 

 This variety is abundant in Carroll and the west part of Bethlehem, as 

 well as in the Hanover area of gneiss. A fourth variety of rock, which 

 may well be associated with the Bethlehem group, is a feldspathic mica 

 schist having large patches of a black mica, the mineral not existing as 

 plates exhibiting easy cleavage, but being an aggregation of crystalline 

 fibres. Other rocks of a foreign character are beds of chloritic schist, 

 with or without magnetite, nearly compact feldspars, quartz, mica, horn- 

 blende, and epidotic schists, and probably beds of limestone. 



The following are observations of the position of the strata in the 

 several parts of the terrane. 



Locality — Bet]ilehem . Dip. 



North of M. Phillips's, 60° N. 22° W. 



East of Peaked hill, N. 22° W. 



South-east side of Round mountain, .... Strike N. 48° E. 



* See Report for 1871 ; also vol. i, p. 33. 

 VOL. IL 14 



