HISTORY OF GEOLOGICAL SURVEY. 45 



is cut off abruptly by the Labrador system at Waterville, crossing at an 

 angle of at least seventy degrees, and as much as fifty degrees in the dip. 

 Another exposure of the same band of gneiss appears at the base of Mt. 

 Carrigain, standing nearly vertically. Passing from this across to the 

 western range, we travel fifteen miles. An anticlinal is hardly supposa- 

 ble over so great a distance. The dips have not been observed system- 

 atically ; but the western range, from the Pemigewasset to Moosilauke, 

 has an anticUnal form, and comes up again west of Moosilauke so as to 

 underlie a synclinal mass of andalusite schist or gneiss. This structure 

 agrees with its position, as deduced from other facts. The andalusite 

 rock is repeated east of the Pemigewasset in an anticlinal way, so as to 

 correspond, as shown by its distribution on the map. 



The porphyritic gneiss west of Echo lake dips north-westerly. At 

 the Lake of the Clouds the dip was not measured. On the ridge running 

 south it dips 50° easterly. Below Walker's falls it stands nearly vertical. 

 Our notes represent a feldspatho-hornblendic rock in horizontal plates 

 immediately contiguous on the east, most likely lying upon the edges of 

 this gneiss. If this proves correct, then the rest of the intermediate 

 space to the crest of the range will be found occupied by the trachytic 

 granite, the horizontal plates showing its beginning. If the horizontal 

 position of the granites and felsites is to be regarded as produced by 

 original deposition, then the elevation of the gneiss took place first ; and 

 this mass of mountains has been only slightly disturbed by elevating 

 forces since that time. 



The porphyritic area along the Ammonoosuc is probably a repetition of 

 that near Echo lake, making a syncUnal axis, just as in Benton, under 

 Moosilauke. With this premise we can infer that the gneiss of Bethlehem 

 was formed subsequently, and lies in a basin, with an east and west axis. 



We cannot as yet locate the andalusite gneiss, save that it is newer than 

 the porphyritic bands, as Shown at Moosilauke. 



There is one further stiggestion in respect to relative ages. The Coos 

 group of Littleton and Lisbon passes around the west end of the Bethle- 

 hem gneiss, showing that the latter existed before either the deposition 

 or elevation of the former. This indicates that the whole of the White 

 Mountain rocks are more ancient than the Coos and Quebec groups of 

 the Connecticut valley. 



