SO-CALLED PORPHYRITIC GNEISS OF NEW’ HAMPSHIRE 703 
Monadnock did not appear to be corroborated by the present 
writer in a somewhat careful study of that region. The mantle 
of glacial drift is there very heavy, but the few outcrops which 
were discovered seemed to prove the bedrock to be of the same 
nature as the schists round about. Again, a visit to Mount 
Osceola showed that the area of porphyritic granite plotted on 
the survey map as occurring on its southern side is really 
occupied by the same coarse-grained hornblende-granite which 
occurs in the bed of Mad River, the ‘‘Conway Granite”’ of the 
survey. , 
So great being the extent of the formation, it was impossible 
in the time at the disposal of the writer to make a close exam- 
ination of all parts of the porphyritic granite. Accordingly, 
most of the observations in the following pages refer to three 
areas, the study of which promised to be most fruitful in the 
problem before us. Those selected were the Winnipiseogee 
area, the Ashuelot area, and the contact of the Main area 
from the town of Jaffrey to Henniker on the Peterboro and 
Hillsboro branch of the Boston and Maine Railroad. We shall 
consider these areas separately, treating of the geological results 
obtained in each along with certain other facts whose arrange- 
ment would be difficult by any other method of discussion. 
Brief description of the porphyritic granite— General macro- 
scopical descriptions of the granite are given in several parts of 
the ‘Geology of New Hampshire.” The rock is remarkably 
simple in its phasal differentiation; so far as a considerable 
collection shows, there are only two important variations in 
it throughout its whole extent. It may be either a porphy- 
ritic granitite or a porphyritic granite proper, and either of 
them may have the foliated structure. They pass into each 
other by insensible gradation in all the areas and it seems to be 
impossible to map them separately. With the exception of this 
and a few other variable features noticed in the sequel, the por- 
phyritic granite is essentially uniform; it is thus possible to dis- 
miss its characterization in a comparatively summary manner. 
In a future paper, the author hopes to give an account of certain 
