SO-CALLED PORPHYRITIC GNEISS OF NEW HAMPSHIRE 7381 
great terrane characterized everywhere by this foliation which 
has been the subject of serious misapprehension among early 
investigators in the state, we shall go into some detail to establish 
this position. 
It was not until the next generation after von Buch* described 
flow-structure in lavas that the phenomenon was studied with 
reference to the origin of gneisses. Scrope? in 1840 and Dar- 
win3 in 1844, closely followed by Naumann,‘ first laid emphasis 
on the truth that ‘dragging movements” on a cooling granitic 
magma may lead to the formation of gneiss. Since that time, a 
host of observations have confirmed their idea so completely 
that it is now possible to frame the most important criteria which 
ought to be applied to a problematical case, and, if satisfied, 
should enforce belief in the gneissic structure of that particular 
instance being of fluxional origin. It is proposed to consider 
briefly these criteria with respect to their validity and to their 
relation to our particular problem. 
I. Since the fluxion-structure is due to differential stress, we 
should expect some parts of a mass, to display a greater excel- 
lences of the foliation. thames others.” “here wall) be zones of 
relatively rapid movement and zones of more static conditions ; 
at least during the geological movement of final consolidation. 
Thus, we may expect to find transitions from trendless granite 
to well-foliated granite or gneiss.5 We have already seen how 
abundantly this change is exemplified in all the areas of the 
porphyritic granite. Both of the State Surveys noted this rela- 
tion between the massive and foliated phases.° The earlier one 
seized upon the former as indicating simply a granite, the second 
tGeognost. Beobacht. auf Reisen durch Deutschland und Italien, 1809, II, p. 209. 
2Trans. Geol. Soc., 2d ser., II, p. 228. 
3 Geological Observations, etc., Ist ed., 1844, ch. iil. 
4Neu. Jahrb., 1847, p. 297. Q.J. Geol. Soc., Notices of Memoirs, p. I. 
5 MICHEL LEvy, Bull. Soc. Geol. de France, 1878-9, p. 852. McMauon, The 
Gneissose-Granite of the Himalayas. Geol. Mag., 1887, p. 214. Jézd., 1888, p. 63. 
HARKER and MARR, The Shap Granite, etc. Q. J. Geol. Soc., 1891, XLVII, p. 284 
EMERSON, Bull. Geol. Soc. Am., I, 1890, p. 559. 
© Note, Geol. of New Hampshire, Vol. II, p. 99. 
