2l8 STRATIGRAPHICAL GEOLOGY, 



between Giant's Stairs and the Mt. Washington river, thus giving it an 

 extension of over three miles in a south-easterly direction. At the north 

 end there is an excellent exposure of the contact between the two forma- 

 tions. It is upon the west bank of the river, two or three hundred feet 

 away from the water, and fifty or sixty feet high. The gneiss is the 

 slightly porphyritic variety of the Montalban schists, dipping 80° N. 80° 

 W., or towards Mt. Clinton, and much disturbed by trap dykes. This 

 position is rendered plain by the stripping of the hillside for more than a 

 hundred feet by a brook. The line of the brook is about twenty-five feet 

 distant from the labradorite rock, with the dip of about twelve degrees 

 south-westerly. The actual junction is covered by earth of little thick- 

 ness. Were one not satisfied with the way in which the formations unite, 

 it would be very easy to observe the actual contact after a little labor ex- 

 pended upon digging. On descending to the river, and over its whole 

 course, the dip of the labradorite is not far removed from horizontal. 

 Next the schists, at the lower end, the masses lie horizontally; then, a 

 few rods above, there is a short synclinal, with the dip of 30°, and after 

 that a nearly horizontal disposition to the northern extremity, where the 

 dip is south-westerly. Fig. 20 shows the junction of the two rocks at 

 the upper end. Perhaps an eighth of a mile above the lower extremity of 

 the formation, there is a seam somewhat resembling a stratum, with a 

 north-west strike, and standing vertically. The rock adjacent on the 

 south is a flinty gneiss, dipping 60° N. 40° W. 



A reexamination of the lower portion of this outlier in 1875 revealed 

 nothing new of any importance. All the ledges are much jointed, and 

 there is a strong contrast between the massive blocks of labradorite and 

 ossipyte and the gneissic rocks adjacent. 



The stratigraphical relations of the two formations seem very simple. 

 The labrador rocks lie unconformably upon the upturned edges of the 

 Montalban gneisses. The discordance varies from forty-five to seventy 

 degrees. In going up the stream, it is easy to see that the labradorite 

 rocks rest upon the gneisses, as both dip in the same direction; and 

 when the upper limit is reached, the dissimilarity between the two is 

 marked fully as strongly as is indicated in the figure. It may be thought, 

 because the labradorite lies in a deep valley, with mountains of gneiss 

 upon both sides, that it must perforce possess an anticlinal structure, and 



