GEOLOGY OF NEW HAMPSH/TRE Si 
the scale of two and one-half miles to the inch, to match the 
Massachusetts work of Simeon Borden in 1842, adding to his. 
delineations approximate contours for every hundred feet. It 
was based upon the United States government map of the inter- 
national boundary (1842), special triangulation under our direc- 
tion, the early and late determinations of the United States coast 
and geodetic survey, combined with detailed compilations from 
the county odometer road surveys. Without pretense to special 
merit, it has been pleasant to us to compare the best parts of this 
map in the White Mountains and the southeast part of the state 
with the beautiful sheets of the United States geological survey,. 
when enlarged to their scale. That experts should at first have 
placed higher value upon this map than it deserved is not the 
fault of its compilers. 
DETERMINATION OF THE ORDER OF THE GROUPS OF SCHISTS. 
In establishing the New Hampshire stratigraphical columm 
the attempt was first made to construct it independently of the 
existence of similar rocks elsewhere. Certain principles were 
accepted as well established. One of them was that crystalline 
schists constitute stratified formations, capable of being identified 
in different districts by their mineral composition. Among the 
groups capable of ready recognition were the following: gneiss,. 
ordinarily consisting of the three constituent minerals, quartz, 
feldspar and mica, with no accessories; and this was termed com- 
mon, or from a locality, Lake Winnipisoegee gneiss. This for con- 
venience was shortened to Lake gneiss, and seemed to be equiv- 
alent to the lower part of the Green Mountain series. In another 
area mica was replaced by chlorite, giving rise to chloritic gneiss,. 
protogene or locally Bethlehem gneiss. Another peculiar variety 
was termed Porphyritic, corresponding to the Augengneiss of Cen- 
tral Europe. The occurrence of large crystals of feldspar seemed 
to be more noticeable than the presence of black spots with the 
white, producing a resemblance to eyes. It was also found that 
sometimes this porphyritic rock was devoid of foliation—the 
crystals were disposed at random instead of being arranged in 
